{"gene":"BICD2","run_date":"2026-06-09T22:02:44","timeline":{"discoveries":[{"year":2013,"finding":"BICD2 disease-causing mutations (p.Ser107Leu, p.Asn188Thr, p.Thr703Met) cause Golgi fragmentation when transiently transfected in HeLa cells, and BICD2 levels are reduced and trapped within the fragmented Golgi in patient fibroblasts, demonstrating the protein's role in maintaining Golgi integrity.","method":"Transient transfection of HeLa cells with mutant BICD2 cDNAs; immunofluorescence of patient fibroblasts","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Strong — single cellular assay (transfection/IF), replicated across three independent studies in same year (PMIDs 23664116, 23664120, 23664119)","pmids":["23664116","23664119","23664120"],"is_preprint":false},{"year":2013,"finding":"BICD2 mutations (p.Ser107Leu and p.Glu774Gly) that cause dominant SMA increase BICD2 binding affinity to the cytoplasmic dynein-dynactin complex; p.Ser107Leu causes accumulation of BICD2 at the MTOC and reduced colocalization with RAB6A, while p.Glu774Gly impairs interaction with RAB6A.","method":"Co-immunoprecipitation; immunofluorescence in HeLa, SH-SY5Y cells and patient lymphoblasts","journal":"American journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — reciprocal Co-IP and IF, single lab, two orthogonal methods","pmids":["23664119","23664120"],"is_preprint":false},{"year":2002,"finding":"BICD2 is phosphorylated by the NIMA-related kinase Nek8 in vitro, and the endogenous proteins associate in vivo; BICD2 localizes to cytoskeletal structures in a microtubule-dependent manner, with nocodazole treatment causing dramatic reorganization of BICD2 correlating with Nek8 phosphorylation.","method":"In vitro kinase assay; co-immunoprecipitation; immunofluorescence with nocodazole treatment","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase assay plus Co-IP plus localization, single lab, multiple orthogonal methods","pmids":["11864968"],"is_preprint":false},{"year":2017,"finding":"Disease-causing BICD2 mutants show enhanced ability to form motile dynein-dynactin-BICD2 (DDB) complexes in vitro; Rab6a-GTP releases BICD2 from an autoinhibited state to promote processive retrograde transport; BICD2 mutants display increased retrograde transport in cells and, when overexpressed in rat hippocampal neurons, decrease neurite growth.","method":"In vitro single-molecule motility assays with purified DDB and Rab6a-GTP; inducible organelle transport assay in cells; neuronal overexpression","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro motility with purified components, multiple orthogonal assays (in vitro + cell-based + neuronal), rigorous controls including liposome-bound Rab6a","pmids":["28883039"],"is_preprint":false},{"year":2015,"finding":"BICD2 functions as a cytosolic factor required for Golgi targeting of Rab6A in semi-intact (SLO-permeabilized) HeLa cells; BICD2 stabilizes the GTP-bound form of Rab6A on Golgi membranes (shown by FRAP), and BICD2/Rab6A play concerted roles in COPI-independent Golgi-to-ER retrograde transport.","method":"Golgi-targeting reconstitution assay in streptolysin O-permeabilized cells; BICD2 knockdown; FRAP analysis of GFP-Rab6A; brefeldin A vesicle transport assay","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical reconstitution in permeabilized cells plus FRAP plus knockdown, single lab, multiple orthogonal methods","pmids":["25962623"],"is_preprint":false},{"year":2018,"finding":"HIV-1 engages BICD2 as a capsid-specific dynein adaptor: purified recombinant BICD2 binds HIV-1 CA assemblies in vitro; depletion of BICD2 by siRNA reduces HIV-1 nuclear DNA accumulation and retrograde viral movement; immunodepletion of BICD2 from cell extracts reduces dynein association with CA assemblies.","method":"siRNA knockdown; in vitro binding assay with purified recombinant BICD2 and CA assemblies; immunodepletion; quantitative nuclear HIV-1 DNA PCR","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with purified protein plus functional siRNA assay plus immunodepletion, single lab but multiple orthogonal methods","pmids":["30068656"],"is_preprint":false},{"year":2018,"finding":"SMALED2-causing BICD2 mutations increase microtubule stability in patient fibroblasts and in motor neurons upon overexpression; in a Drosophila model, neuron-specific expression of BICD2 mutants reduces neuromuscular junction size and impairs locomotion, while muscle-specific expression has no effect.","method":"Microtubule stability assays in patient fibroblasts; Drosophila transgenic neuron/muscle-specific expression; NMJ morphology analysis; locomotion assays","journal":"Human molecular genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell-based functional assay plus in vivo Drosophila model with cell-type specificity, single lab, two orthogonal systems","pmids":["29528393"],"is_preprint":false},{"year":2020,"finding":"BICD2 is required for physiological flow of constitutive secretory cargoes from the Trans Golgi Network to the plasma membrane (VSV-G reporter assay in patient fibroblasts); muscle-specific knockout of Bicd2 in mice reduces L4 ventral motor axons comparably to global knockout, implicating muscle BICD2 in non-cell autonomous motor neuron maintenance.","method":"VSV-G secretory cargo reporter assay in SMALED2 patient fibroblasts; conditional muscle-specific Bicd2 knockout mice; L4 ventral root axon counting","journal":"Acta neuropathologica communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional cargo transport assay plus conditional KO mouse model with quantitative neuroanatomical readout, single lab","pmids":["32183910"],"is_preprint":false},{"year":2020,"finding":"BICD2 localizes to the nuclear envelope (NE) through interaction with Nesprin-2; a truncating BICD2 variant (K775X) disrupts this interaction, prevents NE recruitment of BICD2 and dynein, and causes severe neuronal migration failure without affecting centrosome movement in mouse embryos; restoring NE localization via KASH fusion rescues migration.","method":"In utero electroporation in mouse embryos; co-immunoprecipitation; live imaging of centrosome/nucleus movement; domain fusion rescue experiments","journal":"Acta neuropathologica communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP interaction mapping plus in vivo electroporation with quantitative migration readout plus domain rescue, multiple orthogonal methods, clear mechanistic chain","pmids":["32665036"],"is_preprint":false},{"year":2020,"finding":"Nesprin-2 recruits BicD2 to the nuclear envelope in both migrating neurons and non-mitotic fibroblasts; BicD2 mediates interaction of Nesprin-2 with both dynein and kinesin-1; mutation of the Nesprin-2 LEWD sequence disrupts BicD2 binding; kinesin-1 inhibition accelerates neuronal migration while dynein inhibition blocks forward nuclear movement.","method":"In utero electroporation in rat brain; co-immunoprecipitation; dominant-negative constructs; live imaging of nuclear and centrosome movement","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 2 / Strong — Co-IP plus in vivo electroporation with quantitative migration readout, replicated in two cell types, multiple constructs and controls","pmids":["32619477"],"is_preprint":false},{"year":2019,"finding":"BICD2 is required cell-intrinsically in post-mitotic cortical neurons for bipolar locomotion and radial migration; neuron-specific conditional Bicd2 KO mice show severely impaired radial migration of late-born upper-layer neurons; disease-associated point mutation in the RAB6/RANBP2-binding domain fails to rescue cortical neuron migration.","method":"Neuron-specific conditional Bicd2 KO mice; single-neuron labeling; rescue experiments with WT and mutant BICD2 constructs","journal":"Acta neuropathologica communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with cell-type specificity plus single-neuron labeling plus domain-specific rescue, in vivo mouse model","pmids":["31655624"],"is_preprint":false},{"year":2022,"finding":"In G2, CDK1 phosphorylates BICD2 to promote its interaction with PLK1; PLK1 then phosphorylates a single N-terminal residue of BICD2, causing a structural change that facilitates interaction with dynein and dynactin and formation of active motor complexes; phospho-BICD2 preferentially interacts with CDK1-phosphorylated RanBP2 at the nuclear envelope, driving centrosome tethering and separation in G2/M.","method":"In vitro kinase assays; phospho-specific antibodies; co-immunoprecipitation; BICD2 phospho-mutants; centrosome separation assays in cells","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro kinase assays identifying specific residues plus Co-IP plus phospho-mutant functional assays, multiple orthogonal methods in single rigorous study","pmids":["37105961"],"is_preprint":false},{"year":2022,"finding":"A minimal Nup358 domain (residues 2162-2184) undergoes coil-to-α-helix transition upon BicD2 binding and activates dynein/dynactin/BicD2 for processive motility on microtubules; mutations in this Nup358 'cargo recognition α-helix' decrease Nup358/BicD2 interaction, dynein recruitment, and motility.","method":"NMR titration and CEST; circular dichroism; mutagenesis; in vitro single-molecule motility assay","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structural characterization plus mutagenesis plus in vitro reconstituted motility assay, multiple orthogonal biophysical and functional methods","pmids":["35229716"],"is_preprint":false},{"year":2023,"finding":"Nesprin-2 and RanBP2 compete for BICD2 binding in vitro, and mutually exclusive RanBP2-BICD2 vs. Nesprin-2-BICD2 interactions at the nuclear envelope play successive roles in interkinetic nuclear migration in radial glial progenitors (via RanBP2) and post-mitotic neuronal migration (via Nesprin-2).","method":"In vitro biochemical competition assays; in utero electroporation-based brain developmental assays with BICD2 mutations affecting RanBP2 vs. Nesprin-2 binding","journal":"PLoS genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro competition assay plus in vivo electroporation with multiple BICD2 disease mutations, two orthogonal systems with clear mechanistic dissection","pmids":["36930595"],"is_preprint":false},{"year":2018,"finding":"BicD2 switches cargo selection based on cell cycle phase: it selects Rab6GTP-positive secretory/Golgi vesicles in G1/S (via Rab6GTP binding) and selects the nucleus in G2 (via Nup358 binding); BicD2 and cargo form predominantly 2:2 complexes; the affinity of BicD2 for Nup358 is higher than for Rab6GTP; RanGTP is a negative regulator of the Nup358/BicD2 interaction.","method":"Quantitative binding assays (fluorescence-based); oligomeric state determination; concentration-dependent affinity measurements; RanGTP competition assay","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative biophysical binding assays with defined affinities and stoichiometries, single lab, multiple cargo comparisons","pmids":["30345745"],"is_preprint":false},{"year":2022,"finding":"Full-length human BicD2 undergoes pH-dependent conformational changes; it forms dimers and higher-order oligomers; it binds RanBP2 in biochemical interaction studies; cryo-EM reveals structural flexibility consistent with autoinhibited and activated states.","method":"Recombinant full-length BicD2 production; cryo-EM; biophysical characterization; interaction studies with RanBP2","journal":"Structure (London, England : 1993)","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — cryo-EM structural characterization of full-length protein, single lab, but limited functional validation and no mutagenesis","pmids":["36150379"],"is_preprint":false},{"year":2024,"finding":"BICD2 binds directly to the HPV16 L2 capsid protein during cell entry; a short segment near the C-terminus of L2 mediates direct BICD2 binding in vitro; BICD2 depletion causes HPV accumulation in endosome and TGN and inhibits infection; BICD2 recruits HPV to dynein for transport along the endosome-TGN/Golgi axis.","method":"siRNA knockdown; in vitro binding assays; cell-based HPV entry assays; co-localization studies","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro direct binding plus functional knockdown plus cell-based entry assays, single lab, multiple orthogonal methods","pmids":["38829892"],"is_preprint":false},{"year":2024,"finding":"Rab6a facilitates HPV association with BICD2 and dynein specifically in the TGN (but not endosome) of infected cells; L2 capsid protein binds directly to GTP-Rab6a in vitro; Rab6a knockdown impairs HPV exit from TGN and intra-Golgi transport; cycling between GDP- and GTP-Rab6 states is required.","method":"siRNA knockdown of Rab6a; in vitro L2-Rab6a binding assay; co-immunoprecipitation of HPV with BICD2/dynein in TGN vs endosome fractions; HPV infection assays","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding plus co-IP in specific subcellular fractions plus functional knockdown, single lab","pmids":["39431827"],"is_preprint":false},{"year":2024,"finding":"The binding site of BicD2 for Rab6GTP spans two regions of Rab6 that undergo structural changes upon GDP-to-GTP transition; hydrophobic interface residues are rearranged explaining increased affinity for GTP-bound Rab6; mutations abolishing Rab6GTP binding to BicD2 reduce co-migration and severely diminish motility of Rab6-positive vesicles in cells.","method":"AlphaFold structure prediction; mutagenesis; co-migration assays in cells; live-cell vesicle motility assays","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — computational structural model validated by mutagenesis and cell-based motility assays, single lab","pmids":["38719748"],"is_preprint":false},{"year":2023,"finding":"The Nup358 cargo-recognition α-helix binds to BicD2 between residues 747-774 in an antiparallel manner forming a helical bundle; two intermolecular salt bridges stabilize this interface; a secondary interface involves an intrinsically disordered Nup358 region binding BicD2 residues 774-800, overlapping with the Rab6 binding site, explaining competitive cargo selection.","method":"AlphaFold2 structure prediction; HADDOCK and ClusPro docking; mutagenesis","journal":"Biomolecules","confidence":"Low","confidence_rationale":"Tier 4 / Weak — primarily computational with mutagenesis validation but no direct structural experiment (crystal/NMR/cryo-EM), single lab","pmids":["37892127"],"is_preprint":false},{"year":2023,"finding":"BICD2 interacts with VHL; VHL promotes K48-linked polyubiquitination of BICD2, leading to its proteasomal degradation; BICD2 promotes STAT1 nuclear translocation to facilitate IFNγ signaling and enhance IFNγ-mediated suppression of system Xc-, increasing ferroptosis sensitivity in renal epithelial cells.","method":"Co-immunoprecipitation; ubiquitination assays; overexpression/knockdown experiments; STAT1 nuclear localization assays","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus ubiquitination assay plus functional nuclear translocation readout, single lab, multiple assays","pmids":["37833251"],"is_preprint":false},{"year":2024,"finding":"PCIF1 methyltransferase activity modifies BICD2 mRNA at a specific m6Am site, reducing BICD2 mRNA stability and translation efficiency; BICD2 depletion reduces ciliogenesis; the ciliogenesis defect in PCIF1-depleted cells (which have elevated BICD2) is rescued by BICD2 knockdown.","method":"Quantitative proteomics; siRNA knockdown of PCIF1 and BICD2; single-base LC-MS m6Am site identification; ciliogenesis assays in RPE-1 cells","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — LC-MS site identification plus knockdown epistasis plus functional ciliogenesis readout, single lab, multiple orthogonal methods","pmids":["38526325"],"is_preprint":false},{"year":2025,"finding":"BICD2 promotes ciliogenesis by directly binding CP110 at the mother centriole and facilitating CP110 removal; BICD2 is recruited to the mother centriole during ciliogenesis; BICD2 depletion inhibits CP110 removal and ciliogenesis; CP110 knockdown rescues ciliogenesis in BICD2-depleted cells; zebrafish bicd2 morphants show ciliogenesis defects reversed by bicd2 mRNA or Cp110 depletion.","method":"Co-immunoprecipitation/direct binding assays; siRNA/shRNA knockdown; ciliogenesis assays in RPE-1 cells; zebrafish morpholino knockdown with rescue","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct binding assay plus genetic epistasis (CP110 KD rescues BICD2 KD) plus in vivo zebrafish validation with mRNA rescue, multiple orthogonal methods","pmids":["41102520"],"is_preprint":false},{"year":2025,"finding":"SMALED2-linked BICD2 mutations (including R747C) cause dynein hyperactivation; R747C is deficient in binding HOPS complex components and RANBP2; R747C displays gain-of-function interaction with GRAMD1A leading to its mislocalization; wild-type BICD2 interacts with HOPS complex components as novel cargo.","method":"Interactome mass spectrometry (AP-MS); dynein motility assays; co-immunoprecipitation; immunofluorescence of GRAMD1A localization","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — AP-MS interactome plus motility assays plus localization, single lab, peer-reviewed publication","pmids":["41334889"],"is_preprint":false},{"year":2025,"finding":"BICD2 is a centriolar protein with a dynein-independent role in controlling mother-daughter centriole engagement; BICD2 removal causes premature centriole disengagement in G2/early M and centriole amplification; BICD2 centriolar localization is controlled by phosphorylation.","method":"Live-cell imaging; BICD2 depletion; centriole engagement/disengagement assays; phospho-mutant analysis; centrosome amplification quantification","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — functional KD with quantitative centriole phenotype plus phospho-mutant analysis, single lab, preprint only","pmids":[],"is_preprint":true},{"year":2025,"finding":"PACS1R203W-HDAC6 recruits BICD2 to form a complex that disperses the Golgi and impairs dynein function; BICD2 in this complex reduces dynein initiation frequency and velocity (rescued by HDAC6 inhibition or Lis1 expression), placing BICD2 downstream of the PACS1-HDAC6 axis in dynein-driven Golgi transport.","method":"Co-immunoprecipitation; cargo motility assays; HDAC6 inhibition; Golgi morphology assays; dynein initiation frequency measurements","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus quantitative motility assays plus rescue with HDAC6 inhibition, single lab, multiple orthogonal methods","pmids":["41888583"],"is_preprint":false},{"year":2025,"finding":"Mechanical tension recruits a third dynein motor to DDB complexes via an auxiliary BicD2 adaptor binding the light intermediate chain; complexes with two or three dyneins generate ~7 pN and ~9 pN respectively; under load DDB primarily takes ~8 nm steps.","method":"Single-molecule optical tweezers force measurements; iSCAT tracking; purified DDB complexes from brain lysate","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — single-molecule reconstitution with force measurements, preprint only, single lab","pmids":[],"is_preprint":true}],"current_model":"BICD2 is a coiled-coil dynein cargo adaptor that links the dynein-dynactin motor complex to diverse cargoes (Rab6GTP-positive Golgi/secretory vesicles, the nucleus via Nup358 and Nesprin-2, HIV-1 and HPV capsids) in a cell-cycle-regulated manner; it exists in an autoinhibited state that is released by GTP-loaded Rab6a or by CDK1/PLK1-mediated phosphorylation to form processive DDB complexes; disease-causing mutations hyperactivate DDB motility, destabilize Golgi structure, alter cargo-specific interactomes, and increase microtubule stability, collectively impairing neuronal migration and motor neuron development, while BICD2 also has dynein-independent roles at the mother centriole controlling centriole engagement/duplication licensing and at the mother centriole facilitating CP110 removal to promote ciliogenesis."},"narrative":{"mechanistic_narrative":"BICD2 is a coiled-coil cargo adaptor that links the cytoplasmic dynein-dynactin motor to diverse cargoes and switches its cargo selection across the cell cycle [PMID:30345745]. It is held in an autoinhibited state that is released by GTP-loaded Rab6a to assemble processive dynein-dynactin-BICD2 (DDB) complexes that drive retrograde transport [PMID:28883039]; the Rab6GTP interface is reconfigured by the GDP-to-GTP transition, and disrupting it abolishes BICD2 co-migration with and motility of Rab6-positive secretory vesicles [PMID:38719748]. Through this activity BICD2 stabilizes GTP-Rab6A on Golgi membranes, supports COPI-independent Golgi-to-ER retrograde transport, and is required for constitutive secretory cargo flow from the TGN to the plasma membrane, thereby maintaining Golgi integrity [PMID:25962623, PMID:32183910, PMID:23664116, PMID:23664119, PMID:23664120]. In a cell-cycle-controlled switch, CDK1 and PLK1 phosphorylate BICD2 in G2, releasing autoinhibition and directing it to the nuclear envelope, where it engages CDK1-phosphorylated RanBP2/Nup358 to tether and separate centrosomes [PMID:37105961]; a Nup358 cargo-recognition segment undergoes a coil-to-helix transition that activates DDB motility [PMID:35229716]. At the nuclear envelope BICD2 also binds Nesprin-2, and RanBP2 and Nesprin-2 compete for mutually exclusive BICD2 interactions that drive successive phases of brain development—interkinetic nuclear migration in radial glia via RanBP2 and post-mitotic neuronal migration via Nesprin-2 [PMID:32665036, PMID:32619477, PMID:36930595]. BICD2 additionally serves as a capsid-specific dynein adaptor co-opted by HIV-1 and HPV16 for retrograde transport to the nucleus [PMID:30068656, PMID:38829892], and has dynein-independent centriolar functions: it binds CP110 at the mother centriole to promote its removal and ciliogenesis [PMID:41102520] and controls mother-daughter centriole engagement. Dominant SMALED2/SMA-causing mutations increase BICD2 affinity for dynein-dynactin and hyperactivate DDB motility, increase microtubule stability, and remodel cargo-specific interactomes, impairing neuronal migration and motor neuron development [PMID:23664119, PMID:23664120, PMID:28883039, PMID:29528393, PMID:41334889].","teleology":[{"year":2002,"claim":"Established BICD2 as a microtubule-associated, cytoskeleton-localized protein subject to kinase regulation, raising the question of how its localization is controlled.","evidence":"In vitro Nek8 kinase assay, Co-IP, and immunofluorescence with nocodazole in cells","pmids":["11864968"],"confidence":"Medium","gaps":["No functional consequence of Nek8 phosphorylation defined","No cargo or motor link established at this stage"]},{"year":2013,"claim":"Linked BICD2 to dominant human motor neuron disease and to Golgi maintenance, showing mutations enhance dynein-dynactin binding while altering Rab6A association.","evidence":"Transient transfection of mutant cDNAs and patient fibroblast/lymphoblast IF and Co-IP in HeLa and SH-SY5Y cells","pmids":["23664116","23664119","23664120"],"confidence":"Medium","gaps":["Mechanism linking enhanced dynein binding to disease not resolved","Whether Golgi fragmentation is cause or consequence unclear"]},{"year":2015,"claim":"Defined a biochemical role for BICD2 as a cytosolic factor that targets and stabilizes GTP-Rab6A on Golgi membranes, supporting COPI-independent retrograde transport.","evidence":"Golgi-targeting reconstitution in SLO-permeabilized cells, BICD2 knockdown, and FRAP of GFP-Rab6A","pmids":["25962623"],"confidence":"Medium","gaps":["Did not reconstitute motility with purified dynein","Direct vs. indirect Rab6A stabilization not separated"]},{"year":2017,"claim":"Demonstrated with purified components that BICD2 is autoinhibited and that Rab6a-GTP releases it to form processive DDB complexes, and that disease mutants hyperactivate this motility.","evidence":"In vitro single-molecule motility with purified DDB and liposome-bound Rab6a-GTP, inducible organelle transport, and neuronal overexpression","pmids":["28883039"],"confidence":"High","gaps":["Structural basis of autoinhibition not visualized","How hyperactivation translates to neuronal pathology not fully defined"]},{"year":2018,"claim":"Showed BICD2 cargo selection is cell-cycle-gated—Rab6GTP vesicles in G1/S versus the nucleus via Nup358 in G2—with defined stoichiometry and affinities and RanGTP as a negative regulator.","evidence":"Quantitative fluorescence binding assays, oligomeric state determination, and RanGTP competition","pmids":["30345745"],"confidence":"Medium","gaps":["In vitro affinities not validated against the in-cell switch","Kinase-driven control of the switch not addressed here"]},{"year":2018,"claim":"Extended BICD2's adaptor role to viral hijacking and to disease-relevant cytoskeletal changes, identifying it as a capsid-specific dynein adaptor for HIV-1 and showing mutations increase microtubule stability and impair neuromuscular function.","evidence":"In vitro CA-binding and immunodepletion with siRNA and nuclear DNA PCR for HIV-1; microtubule stability assays and Drosophila neuron/muscle-specific expression for SMALED2","pmids":["30068656","29528393"],"confidence":"High","gaps":["Capsid recognition determinants on BICD2 not mapped","Link between microtubule hyperstability and motor neuron loss mechanistic chain incomplete"]},{"year":2020,"claim":"Resolved the nuclear-envelope arm of BICD2 function, showing Nesprin-2 recruits BICD2 and dynein/kinesin-1 to drive neuronal nuclear migration, and demonstrating cell-intrinsic neuronal and non-cell-autonomous muscle requirements in mice.","evidence":"In utero electroporation in mouse/rat brain, Co-IP and LEWD/KASH mutagenesis, conditional neuron- and muscle-specific Bicd2 KO mice, and VSV-G secretory reporter in patient fibroblasts","pmids":["32665036","32619477","31655624","32183910"],"confidence":"High","gaps":["How dynein/kinesin-1 directional balance is set not fully defined","Molecular basis of non-cell-autonomous muscle contribution unresolved"]},{"year":2022,"claim":"Defined the kinase logic and structural transitions activating BICD2 for nuclear/centrosomal cargo, showing CDK1 then PLK1 phosphorylation switches it to a dynein-competent state engaging phospho-RanBP2, with a Nup358 coil-to-helix transition activating motility.","evidence":"In vitro kinase assays with residue mapping, phospho-mutant centrosome separation assays, NMR/CD on the Nup358 helix, and in vitro single-molecule motility; cryo-EM of full-length BicD2","pmids":["37105961","35229716","36150379"],"confidence":"High","gaps":["High-resolution structure of the activated DDB-BICD2 complex lacking","Full-length cryo-EM gave limited functional/mutagenesis validation"]},{"year":2023,"claim":"Established that mutually exclusive RanBP2 versus Nesprin-2 binding partitions BICD2 between successive developmental tasks, and uncovered a degradation route and a non-transport signaling function.","evidence":"In vitro competition assays and in utero electroporation with binding-selective mutations; VHL ubiquitination/Co-IP and STAT1 nuclear translocation assays; AlphaFold/docking of the Nup358 interface","pmids":["36930595","37833251","37892127"],"confidence":"High","gaps":["Nup358 interface model not confirmed by direct structure (Low-confidence prediction)","How VHL-mediated turnover integrates with cell-cycle regulation unknown"]},{"year":2024,"claim":"Broadened BICD2's cargo repertoire and regulation, identifying HPV16 L2/Rab6a-dependent transport, a refined Rab6GTP interface, and m6Am-mediated mRNA control linking BICD2 to ciliogenesis.","evidence":"In vitro L2/Rab6a binding, siRNA and fractionated Co-IP and entry assays; AlphaFold Rab6 model with mutagenesis and vesicle motility; PCIF1 LC-MS m6Am mapping with knockdown epistasis and ciliogenesis assays","pmids":["38829892","39431827","38719748","38526325"],"confidence":"Medium","gaps":["Rab6GTP interface based on computational model with cell validation only","How m6Am modification tunes BICD2 levels mechanistically incomplete"]},{"year":2025,"claim":"Revealed dynein-independent centriolar functions and further disease/regulatory mechanisms, showing BICD2 binds CP110 to promote ciliogenesis, controls centriole engagement, and that mutations remodel its interactome.","evidence":"Direct CP110 binding with knockdown epistasis and zebrafish rescue; centriole engagement live imaging with phospho-mutants (preprint); AP-MS interactome with motility assays for R747C; PACS1-HDAC6 Co-IP and motility assays","pmids":["41102520","41334889","41888583"],"confidence":"High","gaps":["How a transport adaptor performs dynein-independent centriolar roles mechanistically unclear","Centriole-engagement role rests on preprint without peer review"]},{"year":null,"claim":"How the kinase-, Rab6-, and competition-based regulatory inputs are integrated in vivo to coordinate BICD2's transport and dynein-independent centriolar/ciliary functions, and how disease mutations selectively perturb specific cargo arms, remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified structural model of activated vs. autoinhibited BICD2 with each cargo","Tissue-specific basis of motor neuron vulnerability not established","Mechanism coupling transport adaptor activity to centriole engagement undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[3,8,9,14]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[2,3,6]},{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[5,16,14]}],"localization":[{"term_id":"GO:0005794","term_label":"Golgi apparatus","supporting_discovery_ids":[0,4,7]},{"term_id":"GO:0005635","term_label":"nuclear envelope","supporting_discovery_ids":[8,9,11,13]},{"term_id":"GO:0005815","term_label":"microtubule organizing center","supporting_discovery_ids":[1,22,24]},{"term_id":"GO:0005856","term_label":"cytoskeleton","supporting_discovery_ids":[2]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[3,4,7,18]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[8,9,10,13]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[11,24]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[21,22]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[0,1,6,23]},{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[5,16,17]}],"complexes":["dynein-dynactin-BICD2 (DDB)","HOPS complex (cargo)"],"partners":["DCTN1","RAB6A","RANBP2","SYNE2","CP110","VHL","PLK1","HDAC6"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8TD16","full_name":"Protein bicaudal D homolog 2","aliases":[],"length_aa":824,"mass_kda":93.5,"function":"Acts as an adapter protein linking the dynein motor complex to various cargos and converts dynein from a non-processive to a highly processive motor in the presence of dynactin. Facilitates and stabilizes the interaction between dynein and dynactin and activates dynein processivity (the ability to move along a microtubule for a long distance without falling off the track) (PubMed:25814576). Facilitates the binding of RAB6A to the Golgi by stabilizing its GTP-bound form. Regulates coat complex coatomer protein I (COPI)-independent Golgi-endoplasmic reticulum transport via its interaction with RAB6A and recruitment of the dynein-dynactin motor complex (PubMed:25962623). Contributes to nuclear and centrosomal positioning prior to mitotic entry through regulation of both dynein and kinesin-1. 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(p.Ser107Leu, p.Asn188Thr, p.Thr703Met) cause Golgi fragmentation when transiently transfected in HeLa cells, and BICD2 levels are reduced and trapped within the fragmented Golgi in patient fibroblasts, demonstrating the protein's role in maintaining Golgi integrity.\",\n      \"method\": \"Transient transfection of HeLa cells with mutant BICD2 cDNAs; immunofluorescence of patient fibroblasts\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Strong — single cellular assay (transfection/IF), replicated across three independent studies in same year (PMIDs 23664116, 23664120, 23664119)\",\n      \"pmids\": [\"23664116\", \"23664119\", \"23664120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"BICD2 mutations (p.Ser107Leu and p.Glu774Gly) that cause dominant SMA increase BICD2 binding affinity to the cytoplasmic dynein-dynactin complex; p.Ser107Leu causes accumulation of BICD2 at the MTOC and reduced colocalization with RAB6A, while p.Glu774Gly impairs interaction with RAB6A.\",\n      \"method\": \"Co-immunoprecipitation; immunofluorescence in HeLa, SH-SY5Y cells and patient lymphoblasts\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — reciprocal Co-IP and IF, single lab, two orthogonal methods\",\n      \"pmids\": [\"23664119\", \"23664120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"BICD2 is phosphorylated by the NIMA-related kinase Nek8 in vitro, and the endogenous proteins associate in vivo; BICD2 localizes to cytoskeletal structures in a microtubule-dependent manner, with nocodazole treatment causing dramatic reorganization of BICD2 correlating with Nek8 phosphorylation.\",\n      \"method\": \"In vitro kinase assay; co-immunoprecipitation; immunofluorescence with nocodazole treatment\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase assay plus Co-IP plus localization, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"11864968\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Disease-causing BICD2 mutants show enhanced ability to form motile dynein-dynactin-BICD2 (DDB) complexes in vitro; Rab6a-GTP releases BICD2 from an autoinhibited state to promote processive retrograde transport; BICD2 mutants display increased retrograde transport in cells and, when overexpressed in rat hippocampal neurons, decrease neurite growth.\",\n      \"method\": \"In vitro single-molecule motility assays with purified DDB and Rab6a-GTP; inducible organelle transport assay in cells; neuronal overexpression\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro motility with purified components, multiple orthogonal assays (in vitro + cell-based + neuronal), rigorous controls including liposome-bound Rab6a\",\n      \"pmids\": [\"28883039\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"BICD2 functions as a cytosolic factor required for Golgi targeting of Rab6A in semi-intact (SLO-permeabilized) HeLa cells; BICD2 stabilizes the GTP-bound form of Rab6A on Golgi membranes (shown by FRAP), and BICD2/Rab6A play concerted roles in COPI-independent Golgi-to-ER retrograde transport.\",\n      \"method\": \"Golgi-targeting reconstitution assay in streptolysin O-permeabilized cells; BICD2 knockdown; FRAP analysis of GFP-Rab6A; brefeldin A vesicle transport assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical reconstitution in permeabilized cells plus FRAP plus knockdown, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"25962623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"HIV-1 engages BICD2 as a capsid-specific dynein adaptor: purified recombinant BICD2 binds HIV-1 CA assemblies in vitro; depletion of BICD2 by siRNA reduces HIV-1 nuclear DNA accumulation and retrograde viral movement; immunodepletion of BICD2 from cell extracts reduces dynein association with CA assemblies.\",\n      \"method\": \"siRNA knockdown; in vitro binding assay with purified recombinant BICD2 and CA assemblies; immunodepletion; quantitative nuclear HIV-1 DNA PCR\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with purified protein plus functional siRNA assay plus immunodepletion, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"30068656\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"SMALED2-causing BICD2 mutations increase microtubule stability in patient fibroblasts and in motor neurons upon overexpression; in a Drosophila model, neuron-specific expression of BICD2 mutants reduces neuromuscular junction size and impairs locomotion, while muscle-specific expression has no effect.\",\n      \"method\": \"Microtubule stability assays in patient fibroblasts; Drosophila transgenic neuron/muscle-specific expression; NMJ morphology analysis; locomotion assays\",\n      \"journal\": \"Human molecular genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell-based functional assay plus in vivo Drosophila model with cell-type specificity, single lab, two orthogonal systems\",\n      \"pmids\": [\"29528393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"BICD2 is required for physiological flow of constitutive secretory cargoes from the Trans Golgi Network to the plasma membrane (VSV-G reporter assay in patient fibroblasts); muscle-specific knockout of Bicd2 in mice reduces L4 ventral motor axons comparably to global knockout, implicating muscle BICD2 in non-cell autonomous motor neuron maintenance.\",\n      \"method\": \"VSV-G secretory cargo reporter assay in SMALED2 patient fibroblasts; conditional muscle-specific Bicd2 knockout mice; L4 ventral root axon counting\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional cargo transport assay plus conditional KO mouse model with quantitative neuroanatomical readout, single lab\",\n      \"pmids\": [\"32183910\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"BICD2 localizes to the nuclear envelope (NE) through interaction with Nesprin-2; a truncating BICD2 variant (K775X) disrupts this interaction, prevents NE recruitment of BICD2 and dynein, and causes severe neuronal migration failure without affecting centrosome movement in mouse embryos; restoring NE localization via KASH fusion rescues migration.\",\n      \"method\": \"In utero electroporation in mouse embryos; co-immunoprecipitation; live imaging of centrosome/nucleus movement; domain fusion rescue experiments\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP interaction mapping plus in vivo electroporation with quantitative migration readout plus domain rescue, multiple orthogonal methods, clear mechanistic chain\",\n      \"pmids\": [\"32665036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nesprin-2 recruits BicD2 to the nuclear envelope in both migrating neurons and non-mitotic fibroblasts; BicD2 mediates interaction of Nesprin-2 with both dynein and kinesin-1; mutation of the Nesprin-2 LEWD sequence disrupts BicD2 binding; kinesin-1 inhibition accelerates neuronal migration while dynein inhibition blocks forward nuclear movement.\",\n      \"method\": \"In utero electroporation in rat brain; co-immunoprecipitation; dominant-negative constructs; live imaging of nuclear and centrosome movement\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — Co-IP plus in vivo electroporation with quantitative migration readout, replicated in two cell types, multiple constructs and controls\",\n      \"pmids\": [\"32619477\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"BICD2 is required cell-intrinsically in post-mitotic cortical neurons for bipolar locomotion and radial migration; neuron-specific conditional Bicd2 KO mice show severely impaired radial migration of late-born upper-layer neurons; disease-associated point mutation in the RAB6/RANBP2-binding domain fails to rescue cortical neuron migration.\",\n      \"method\": \"Neuron-specific conditional Bicd2 KO mice; single-neuron labeling; rescue experiments with WT and mutant BICD2 constructs\",\n      \"journal\": \"Acta neuropathologica communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with cell-type specificity plus single-neuron labeling plus domain-specific rescue, in vivo mouse model\",\n      \"pmids\": [\"31655624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In G2, CDK1 phosphorylates BICD2 to promote its interaction with PLK1; PLK1 then phosphorylates a single N-terminal residue of BICD2, causing a structural change that facilitates interaction with dynein and dynactin and formation of active motor complexes; phospho-BICD2 preferentially interacts with CDK1-phosphorylated RanBP2 at the nuclear envelope, driving centrosome tethering and separation in G2/M.\",\n      \"method\": \"In vitro kinase assays; phospho-specific antibodies; co-immunoprecipitation; BICD2 phospho-mutants; centrosome separation assays in cells\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro kinase assays identifying specific residues plus Co-IP plus phospho-mutant functional assays, multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"37105961\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A minimal Nup358 domain (residues 2162-2184) undergoes coil-to-α-helix transition upon BicD2 binding and activates dynein/dynactin/BicD2 for processive motility on microtubules; mutations in this Nup358 'cargo recognition α-helix' decrease Nup358/BicD2 interaction, dynein recruitment, and motility.\",\n      \"method\": \"NMR titration and CEST; circular dichroism; mutagenesis; in vitro single-molecule motility assay\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structural characterization plus mutagenesis plus in vitro reconstituted motility assay, multiple orthogonal biophysical and functional methods\",\n      \"pmids\": [\"35229716\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Nesprin-2 and RanBP2 compete for BICD2 binding in vitro, and mutually exclusive RanBP2-BICD2 vs. Nesprin-2-BICD2 interactions at the nuclear envelope play successive roles in interkinetic nuclear migration in radial glial progenitors (via RanBP2) and post-mitotic neuronal migration (via Nesprin-2).\",\n      \"method\": \"In vitro biochemical competition assays; in utero electroporation-based brain developmental assays with BICD2 mutations affecting RanBP2 vs. Nesprin-2 binding\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro competition assay plus in vivo electroporation with multiple BICD2 disease mutations, two orthogonal systems with clear mechanistic dissection\",\n      \"pmids\": [\"36930595\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"BicD2 switches cargo selection based on cell cycle phase: it selects Rab6GTP-positive secretory/Golgi vesicles in G1/S (via Rab6GTP binding) and selects the nucleus in G2 (via Nup358 binding); BicD2 and cargo form predominantly 2:2 complexes; the affinity of BicD2 for Nup358 is higher than for Rab6GTP; RanGTP is a negative regulator of the Nup358/BicD2 interaction.\",\n      \"method\": \"Quantitative binding assays (fluorescence-based); oligomeric state determination; concentration-dependent affinity measurements; RanGTP competition assay\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative biophysical binding assays with defined affinities and stoichiometries, single lab, multiple cargo comparisons\",\n      \"pmids\": [\"30345745\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Full-length human BicD2 undergoes pH-dependent conformational changes; it forms dimers and higher-order oligomers; it binds RanBP2 in biochemical interaction studies; cryo-EM reveals structural flexibility consistent with autoinhibited and activated states.\",\n      \"method\": \"Recombinant full-length BicD2 production; cryo-EM; biophysical characterization; interaction studies with RanBP2\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — cryo-EM structural characterization of full-length protein, single lab, but limited functional validation and no mutagenesis\",\n      \"pmids\": [\"36150379\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"BICD2 binds directly to the HPV16 L2 capsid protein during cell entry; a short segment near the C-terminus of L2 mediates direct BICD2 binding in vitro; BICD2 depletion causes HPV accumulation in endosome and TGN and inhibits infection; BICD2 recruits HPV to dynein for transport along the endosome-TGN/Golgi axis.\",\n      \"method\": \"siRNA knockdown; in vitro binding assays; cell-based HPV entry assays; co-localization studies\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro direct binding plus functional knockdown plus cell-based entry assays, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38829892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Rab6a facilitates HPV association with BICD2 and dynein specifically in the TGN (but not endosome) of infected cells; L2 capsid protein binds directly to GTP-Rab6a in vitro; Rab6a knockdown impairs HPV exit from TGN and intra-Golgi transport; cycling between GDP- and GTP-Rab6 states is required.\",\n      \"method\": \"siRNA knockdown of Rab6a; in vitro L2-Rab6a binding assay; co-immunoprecipitation of HPV with BICD2/dynein in TGN vs endosome fractions; HPV infection assays\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding plus co-IP in specific subcellular fractions plus functional knockdown, single lab\",\n      \"pmids\": [\"39431827\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The binding site of BicD2 for Rab6GTP spans two regions of Rab6 that undergo structural changes upon GDP-to-GTP transition; hydrophobic interface residues are rearranged explaining increased affinity for GTP-bound Rab6; mutations abolishing Rab6GTP binding to BicD2 reduce co-migration and severely diminish motility of Rab6-positive vesicles in cells.\",\n      \"method\": \"AlphaFold structure prediction; mutagenesis; co-migration assays in cells; live-cell vesicle motility assays\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — computational structural model validated by mutagenesis and cell-based motility assays, single lab\",\n      \"pmids\": [\"38719748\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"The Nup358 cargo-recognition α-helix binds to BicD2 between residues 747-774 in an antiparallel manner forming a helical bundle; two intermolecular salt bridges stabilize this interface; a secondary interface involves an intrinsically disordered Nup358 region binding BicD2 residues 774-800, overlapping with the Rab6 binding site, explaining competitive cargo selection.\",\n      \"method\": \"AlphaFold2 structure prediction; HADDOCK and ClusPro docking; mutagenesis\",\n      \"journal\": \"Biomolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Weak — primarily computational with mutagenesis validation but no direct structural experiment (crystal/NMR/cryo-EM), single lab\",\n      \"pmids\": [\"37892127\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"BICD2 interacts with VHL; VHL promotes K48-linked polyubiquitination of BICD2, leading to its proteasomal degradation; BICD2 promotes STAT1 nuclear translocation to facilitate IFNγ signaling and enhance IFNγ-mediated suppression of system Xc-, increasing ferroptosis sensitivity in renal epithelial cells.\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays; overexpression/knockdown experiments; STAT1 nuclear localization assays\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus ubiquitination assay plus functional nuclear translocation readout, single lab, multiple assays\",\n      \"pmids\": [\"37833251\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PCIF1 methyltransferase activity modifies BICD2 mRNA at a specific m6Am site, reducing BICD2 mRNA stability and translation efficiency; BICD2 depletion reduces ciliogenesis; the ciliogenesis defect in PCIF1-depleted cells (which have elevated BICD2) is rescued by BICD2 knockdown.\",\n      \"method\": \"Quantitative proteomics; siRNA knockdown of PCIF1 and BICD2; single-base LC-MS m6Am site identification; ciliogenesis assays in RPE-1 cells\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — LC-MS site identification plus knockdown epistasis plus functional ciliogenesis readout, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38526325\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"BICD2 promotes ciliogenesis by directly binding CP110 at the mother centriole and facilitating CP110 removal; BICD2 is recruited to the mother centriole during ciliogenesis; BICD2 depletion inhibits CP110 removal and ciliogenesis; CP110 knockdown rescues ciliogenesis in BICD2-depleted cells; zebrafish bicd2 morphants show ciliogenesis defects reversed by bicd2 mRNA or Cp110 depletion.\",\n      \"method\": \"Co-immunoprecipitation/direct binding assays; siRNA/shRNA knockdown; ciliogenesis assays in RPE-1 cells; zebrafish morpholino knockdown with rescue\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct binding assay plus genetic epistasis (CP110 KD rescues BICD2 KD) plus in vivo zebrafish validation with mRNA rescue, multiple orthogonal methods\",\n      \"pmids\": [\"41102520\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"SMALED2-linked BICD2 mutations (including R747C) cause dynein hyperactivation; R747C is deficient in binding HOPS complex components and RANBP2; R747C displays gain-of-function interaction with GRAMD1A leading to its mislocalization; wild-type BICD2 interacts with HOPS complex components as novel cargo.\",\n      \"method\": \"Interactome mass spectrometry (AP-MS); dynein motility assays; co-immunoprecipitation; immunofluorescence of GRAMD1A localization\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — AP-MS interactome plus motility assays plus localization, single lab, peer-reviewed publication\",\n      \"pmids\": [\"41334889\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"BICD2 is a centriolar protein with a dynein-independent role in controlling mother-daughter centriole engagement; BICD2 removal causes premature centriole disengagement in G2/early M and centriole amplification; BICD2 centriolar localization is controlled by phosphorylation.\",\n      \"method\": \"Live-cell imaging; BICD2 depletion; centriole engagement/disengagement assays; phospho-mutant analysis; centrosome amplification quantification\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — functional KD with quantitative centriole phenotype plus phospho-mutant analysis, single lab, preprint only\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PACS1R203W-HDAC6 recruits BICD2 to form a complex that disperses the Golgi and impairs dynein function; BICD2 in this complex reduces dynein initiation frequency and velocity (rescued by HDAC6 inhibition or Lis1 expression), placing BICD2 downstream of the PACS1-HDAC6 axis in dynein-driven Golgi transport.\",\n      \"method\": \"Co-immunoprecipitation; cargo motility assays; HDAC6 inhibition; Golgi morphology assays; dynein initiation frequency measurements\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus quantitative motility assays plus rescue with HDAC6 inhibition, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"41888583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Mechanical tension recruits a third dynein motor to DDB complexes via an auxiliary BicD2 adaptor binding the light intermediate chain; complexes with two or three dyneins generate ~7 pN and ~9 pN respectively; under load DDB primarily takes ~8 nm steps.\",\n      \"method\": \"Single-molecule optical tweezers force measurements; iSCAT tracking; purified DDB complexes from brain lysate\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — single-molecule reconstitution with force measurements, preprint only, single lab\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"BICD2 is a coiled-coil dynein cargo adaptor that links the dynein-dynactin motor complex to diverse cargoes (Rab6GTP-positive Golgi/secretory vesicles, the nucleus via Nup358 and Nesprin-2, HIV-1 and HPV capsids) in a cell-cycle-regulated manner; it exists in an autoinhibited state that is released by GTP-loaded Rab6a or by CDK1/PLK1-mediated phosphorylation to form processive DDB complexes; disease-causing mutations hyperactivate DDB motility, destabilize Golgi structure, alter cargo-specific interactomes, and increase microtubule stability, collectively impairing neuronal migration and motor neuron development, while BICD2 also has dynein-independent roles at the mother centriole controlling centriole engagement/duplication licensing and at the mother centriole facilitating CP110 removal to promote ciliogenesis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"BICD2 is a coiled-coil cargo adaptor that links the cytoplasmic dynein-dynactin motor to diverse cargoes and switches its cargo selection across the cell cycle [#14]. It is held in an autoinhibited state that is released by GTP-loaded Rab6a to assemble processive dynein-dynactin-BICD2 (DDB) complexes that drive retrograde transport [#3]; the Rab6GTP interface is reconfigured by the GDP-to-GTP transition, and disrupting it abolishes BICD2 co-migration with and motility of Rab6-positive secretory vesicles [#18]. Through this activity BICD2 stabilizes GTP-Rab6A on Golgi membranes, supports COPI-independent Golgi-to-ER retrograde transport, and is required for constitutive secretory cargo flow from the TGN to the plasma membrane, thereby maintaining Golgi integrity [#4, #7, #0]. In a cell-cycle-controlled switch, CDK1 and PLK1 phosphorylate BICD2 in G2, releasing autoinhibition and directing it to the nuclear envelope, where it engages CDK1-phosphorylated RanBP2/Nup358 to tether and separate centrosomes [#11]; a Nup358 cargo-recognition segment undergoes a coil-to-helix transition that activates DDB motility [#12]. At the nuclear envelope BICD2 also binds Nesprin-2, and RanBP2 and Nesprin-2 compete for mutually exclusive BICD2 interactions that drive successive phases of brain development—interkinetic nuclear migration in radial glia via RanBP2 and post-mitotic neuronal migration via Nesprin-2 [#8, #9, #13]. BICD2 additionally serves as a capsid-specific dynein adaptor co-opted by HIV-1 and HPV16 for retrograde transport to the nucleus [#5, #16], and has dynein-independent centriolar functions: it binds CP110 at the mother centriole to promote its removal and ciliogenesis [#22] and controls mother-daughter centriole engagement [#24]. Dominant SMALED2/SMA-causing mutations increase BICD2 affinity for dynein-dynactin and hyperactivate DDB motility, increase microtubule stability, and remodel cargo-specific interactomes, impairing neuronal migration and motor neuron development [#1, #3, #6, #23].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established BICD2 as a microtubule-associated, cytoskeleton-localized protein subject to kinase regulation, raising the question of how its localization is controlled.\",\n      \"evidence\": \"In vitro Nek8 kinase assay, Co-IP, and immunofluorescence with nocodazole in cells\",\n      \"pmids\": [\"11864968\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No functional consequence of Nek8 phosphorylation defined\", \"No cargo or motor link established at this stage\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Linked BICD2 to dominant human motor neuron disease and to Golgi maintenance, showing mutations enhance dynein-dynactin binding while altering Rab6A association.\",\n      \"evidence\": \"Transient transfection of mutant cDNAs and patient fibroblast/lymphoblast IF and Co-IP in HeLa and SH-SY5Y cells\",\n      \"pmids\": [\"23664116\", \"23664119\", \"23664120\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism linking enhanced dynein binding to disease not resolved\", \"Whether Golgi fragmentation is cause or consequence unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined a biochemical role for BICD2 as a cytosolic factor that targets and stabilizes GTP-Rab6A on Golgi membranes, supporting COPI-independent retrograde transport.\",\n      \"evidence\": \"Golgi-targeting reconstitution in SLO-permeabilized cells, BICD2 knockdown, and FRAP of GFP-Rab6A\",\n      \"pmids\": [\"25962623\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not reconstitute motility with purified dynein\", \"Direct vs. indirect Rab6A stabilization not separated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated with purified components that BICD2 is autoinhibited and that Rab6a-GTP releases it to form processive DDB complexes, and that disease mutants hyperactivate this motility.\",\n      \"evidence\": \"In vitro single-molecule motility with purified DDB and liposome-bound Rab6a-GTP, inducible organelle transport, and neuronal overexpression\",\n      \"pmids\": [\"28883039\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of autoinhibition not visualized\", \"How hyperactivation translates to neuronal pathology not fully defined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed BICD2 cargo selection is cell-cycle-gated—Rab6GTP vesicles in G1/S versus the nucleus via Nup358 in G2—with defined stoichiometry and affinities and RanGTP as a negative regulator.\",\n      \"evidence\": \"Quantitative fluorescence binding assays, oligomeric state determination, and RanGTP competition\",\n      \"pmids\": [\"30345745\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vitro affinities not validated against the in-cell switch\", \"Kinase-driven control of the switch not addressed here\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Extended BICD2's adaptor role to viral hijacking and to disease-relevant cytoskeletal changes, identifying it as a capsid-specific dynein adaptor for HIV-1 and showing mutations increase microtubule stability and impair neuromuscular function.\",\n      \"evidence\": \"In vitro CA-binding and immunodepletion with siRNA and nuclear DNA PCR for HIV-1; microtubule stability assays and Drosophila neuron/muscle-specific expression for SMALED2\",\n      \"pmids\": [\"30068656\", \"29528393\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Capsid recognition determinants on BICD2 not mapped\", \"Link between microtubule hyperstability and motor neuron loss mechanistic chain incomplete\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the nuclear-envelope arm of BICD2 function, showing Nesprin-2 recruits BICD2 and dynein/kinesin-1 to drive neuronal nuclear migration, and demonstrating cell-intrinsic neuronal and non-cell-autonomous muscle requirements in mice.\",\n      \"evidence\": \"In utero electroporation in mouse/rat brain, Co-IP and LEWD/KASH mutagenesis, conditional neuron- and muscle-specific Bicd2 KO mice, and VSV-G secretory reporter in patient fibroblasts\",\n      \"pmids\": [\"32665036\", \"32619477\", \"31655624\", \"32183910\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How dynein/kinesin-1 directional balance is set not fully defined\", \"Molecular basis of non-cell-autonomous muscle contribution unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined the kinase logic and structural transitions activating BICD2 for nuclear/centrosomal cargo, showing CDK1 then PLK1 phosphorylation switches it to a dynein-competent state engaging phospho-RanBP2, with a Nup358 coil-to-helix transition activating motility.\",\n      \"evidence\": \"In vitro kinase assays with residue mapping, phospho-mutant centrosome separation assays, NMR/CD on the Nup358 helix, and in vitro single-molecule motility; cryo-EM of full-length BicD2\",\n      \"pmids\": [\"37105961\", \"35229716\", \"36150379\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the activated DDB-BICD2 complex lacking\", \"Full-length cryo-EM gave limited functional/mutagenesis validation\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established that mutually exclusive RanBP2 versus Nesprin-2 binding partitions BICD2 between successive developmental tasks, and uncovered a degradation route and a non-transport signaling function.\",\n      \"evidence\": \"In vitro competition assays and in utero electroporation with binding-selective mutations; VHL ubiquitination/Co-IP and STAT1 nuclear translocation assays; AlphaFold/docking of the Nup358 interface\",\n      \"pmids\": [\"36930595\", \"37833251\", \"37892127\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nup358 interface model not confirmed by direct structure (Low-confidence prediction)\", \"How VHL-mediated turnover integrates with cell-cycle regulation unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Broadened BICD2's cargo repertoire and regulation, identifying HPV16 L2/Rab6a-dependent transport, a refined Rab6GTP interface, and m6Am-mediated mRNA control linking BICD2 to ciliogenesis.\",\n      \"evidence\": \"In vitro L2/Rab6a binding, siRNA and fractionated Co-IP and entry assays; AlphaFold Rab6 model with mutagenesis and vesicle motility; PCIF1 LC-MS m6Am mapping with knockdown epistasis and ciliogenesis assays\",\n      \"pmids\": [\"38829892\", \"39431827\", \"38719748\", \"38526325\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Rab6GTP interface based on computational model with cell validation only\", \"How m6Am modification tunes BICD2 levels mechanistically incomplete\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Revealed dynein-independent centriolar functions and further disease/regulatory mechanisms, showing BICD2 binds CP110 to promote ciliogenesis, controls centriole engagement, and that mutations remodel its interactome.\",\n      \"evidence\": \"Direct CP110 binding with knockdown epistasis and zebrafish rescue; centriole engagement live imaging with phospho-mutants (preprint); AP-MS interactome with motility assays for R747C; PACS1-HDAC6 Co-IP and motility assays\",\n      \"pmids\": [\"41102520\", \"41334889\", \"41888583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How a transport adaptor performs dynein-independent centriolar roles mechanistically unclear\", \"Centriole-engagement role rests on preprint without peer review\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the kinase-, Rab6-, and competition-based regulatory inputs are integrated in vivo to coordinate BICD2's transport and dynein-independent centriolar/ciliary functions, and how disease mutations selectively perturb specific cargo arms, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified structural model of activated vs. autoinhibited BICD2 with each cargo\", \"Tissue-specific basis of motor neuron vulnerability not established\", \"Mechanism coupling transport adaptor activity to centriole engagement undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [3, 8, 9, 14]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [2, 3, 6]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [5, 16, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005794\", \"supporting_discovery_ids\": [0, 4, 7]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [8, 9, 11, 13]},\n      {\"term_id\": \"GO:0005815\", \"supporting_discovery_ids\": [1, 22, 24]},\n      {\"term_id\": \"GO:0005856\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [3, 4, 7, 18]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [8, 9, 10, 13]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [11, 24]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [21, 22]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [0, 1, 6, 23]},\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [5, 16, 17]}\n    ],\n    \"complexes\": [\"dynein-dynactin-BICD2 (DDB)\", \"HOPS complex (cargo)\"],\n    \"partners\": [\"DCTN1\", \"RAB6A\", \"RANBP2\", \"SYNE2\", \"CP110\", \"VHL\", \"PLK1\", \"HDAC6\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}