Affinage

AP3B1

AP-3 complex subunit beta-1 · UniProt O00203

Length
1094 aa
Mass
121.3 kDa
Annotated
2026-06-09
23 papers in source corpus 11 papers cited in narrative 11 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

AP3B1 encodes the β3A subunit of the heterotetrameric AP-3 adaptor complex, which mediates the direct sorting of integral membrane cargo from the trans-Golgi network/endosomal system to lysosomes and lysosome-related organelles (PMID:9931340, PMID:11809908). Loss of AP3B1 destabilizes the complex—co-depleting the associated μ3 subunit (PMID:11809908)—and reroutes lysosomal membrane proteins including LAMP-1, LAMP-2, LAMP-3, CD63, and the melanosomal protein tyrosinase to the plasma membrane, demonstrating that AP3B1 enforces a direct intracellular routing pathway distinct from a default surface route (PMID:11058094, PMID:11809908, PMID:16537806). Through this trafficking function AP3B1 is required for the biogenesis and function of multiple lysosome-related organelles: defects cause hypopigmented melanosomes, impaired platelet dense granules, and defective cytotoxic T-lymphocyte secretory lysosomes, the cellular basis of the pearl phenotype and Hermansky-Pudlak-type disease (PMID:9931340, PMID:19679886). Genetic studies place AP3B1 in a pathway distinct from but synergistic with HPS1 for ocular melanosome biogenesis (PMID:25160823). AP3B1 is a substrate for IP7-mediated pyrophosphorylation on a prephosphorylated serine, and this modification modulates its interaction with the kinesin motor Kif3A (PMID:19934039). Beyond canonical trafficking, AP3B1 functions in antiviral defense, physically interacting with the SARS-CoV-2 envelope protein to restrict viral replication (PMID:39339853) and acting with PDIA3/ERP57 in selective autophagy-mediated degradation of the rabies virus G protein (PMID:39128851).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 1999 High

    Established AP3B1 as a core AP-3 adaptor subunit whose loss disrupts biogenesis of lysosomes, melanosomes, and platelet-dense granules, defining its identity as a trafficking gene.

    Evidence Positional/candidate cloning and mutation identification in two pearl alleles, with expression analysis

    PMID:9931340

    Open questions at the time
    • Did not resolve the molecular sorting step (direct vs. alternate routing)
    • No cargo-level trafficking assay
  2. 2000 High

    Confirmed AP3B1 as the causal pearl gene and showed loss mislocalizes LAMP-I, LAMP-II, and tyrosinase to the cell surface, revealing an alternate plasma-membrane route for AP-3 cargo.

    Evidence Homologous-recombination knockout mice with compound heterozygote rescue and immunofluorescence cargo localization

    PMID:11058094

    Open questions at the time
    • Did not address effects on other AP-3 subunits
    • Mechanism of the alternate route not defined
  3. 2002 High

    Demonstrated in human null patient cells that loss of β3A co-depletes the μ3 subunit and aberrantly routes LAMP-3 to the plasma membrane, establishing AP3B1 as required for direct TGN-to-lysosome cargo delivery.

    Evidence Patient fibroblast immunoblotting for AP-3 subunits and cell-surface trafficking assay for LAMP-3

    PMID:11809908

    Open questions at the time
    • Did not map the cargo-recognition determinants
    • Structural basis of complex destabilization not shown
  4. 2006 High

    Showed that an in-frame exon-skipping deletion perturbs AP-3 heterotetramer assembly and misroutes CD63, linking complex integrity to cargo sorting and to rapid degradation of immature melanosomes in keratinocytes.

    Evidence Patient genetics with CD63 immunofluorescence trafficking assay and electron microscopy

    PMID:16537806

    Open questions at the time
    • Single-lab functional data
    • Fate of misrouted CD63 not fully tracked
  5. 2009 Medium

    Identified a post-translational regulatory layer: AP3B1 is pyrophosphorylated by IP7 on a prephosphorylated serine, and this modulates binding to the kinesin Kif3A, coupling AP-3 to motor-driven trafficking.

    Evidence In vitro IP7 pyrophosphorylation assay, AP3B1-Kif3A co-immunoprecipitation, and HIV-1 VLP release assay

    PMID:19934039

    Open questions at the time
    • Single lab; in vitro pyrophosphorylation
    • Functional consequence of Kif3A binding in vivo not fully resolved
  6. 2009 Medium

    Extended the lysosome-related organelle role to immune and hemostatic cells, showing AP3B1 loss impairs CTL secretory-lysosome function and platelet dense granule activity.

    Evidence Patient-derived CTL clones (CD63 surface, cytotoxicity) and platelet aggregation/serotonin uptake assays

    PMID:19679886

    Open questions at the time
    • Single lab
    • Biogenesis vs. secretion defect not disentangled
  7. 2004 Medium

    Characterized a canine AP3B1 frameshift in a homopolymeric tract as the cause of cyclic neutropenia, with transcriptional slippage producing mixed transcripts, illustrating mutational mechanism in this gene.

    Evidence RT-PCR subclone analysis and in vitro reporter assay for transcriptional slippage

    PMID:15576359

    Open questions at the time
    • Mechanistic link to neutrophil cycling not established
    • Model-organism mutation, not human cargo biology
  8. 2014 Medium

    Genetic epistasis placed AP3B1 and HPS1 in distinct but synergistic pathways for ocular melanosome biogenesis and tyrosinase distribution.

    Evidence Single and double mutant mouse pigmentation analysis, tyrosinase activity assay, histology

    PMID:25160823

    Open questions at the time
    • Molecular basis of pathway divergence not defined
    • Single lab
  9. 2019 Low

    Implicated AP3B1 in male reproductive development, with pearl mice showing delayed testis development and reduced Sertoli-cell lysosomes.

    Evidence Phenotypic characterization of mutant mice (sperm count, testosterone, EM)

    PMID:30786955

    Open questions at the time
    • No direct molecular mechanism shown
    • Single lab phenotypic study
    • Lysosome defect causal link not established
  10. 2024 Medium

    Revealed an antiviral role: AP3B1 interacts with the SARS-CoV-2 E protein and restricts replication, and acts with PDIA3 to drive selective autophagy of the rabies virus G protein.

    Evidence IP/IFA in infected cells with gain/loss-of-function viral output; AP-MS, Co-IP, and KO functional assay for RABV G degradation

    PMID:39128851 PMID:39339853

    Open questions at the time
    • Mechanistic link between trafficking function and viral restriction not defined
    • Single lab per virus
    • Whether AP-3 complex integrity is required not tested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How AP-3 cargo-recognition specificity, IP7/Kif3A regulation, and the newly described antiviral functions integrate at the structural and pathway level remains unresolved.
  • No structural model of the AP-3 cargo-binding interface in the timeline
  • Mechanism connecting trafficking to viral restriction unknown
  • In vivo role of pyrophosphorylation undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0038024 cargo receptor activity 3 GO:0060090 molecular adaptor activity 2
Localization
GO:0005764 lysosome 2 GO:0005794 Golgi apparatus 2 GO:0005768 endosome 1
Pathway
R-HSA-9609507 Protein localization 4 R-HSA-1852241 Organelle biogenesis and maintenance 3 R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-9612973 Autophagy 1
Partners
AP3M1KIF3APDIA3
Complex memberships
AP-3 adaptor complex

Evidence

Reading pass · 11 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 AP3B1 (beta3A subunit) is a core component of the AP-3 adaptor complex that regulates protein trafficking in the trans-Golgi network/endosomal compartments; mutations (large internal tandem duplication and deletion) in two pearl alleles abrogate beta3A function, causing defective biogenesis of lysosomes, melanosomes, and platelet-dense granules. Positional/candidate cloning, mutation identification in two alleles, expression analysis in kidney tissue Human molecular genetics High 9931340
2000 Homologous-recombination knockout of Ap3b1 in mice confirms it is the causal gene for the pearl phenotype; loss of AP3B1 causes mislocalization of lysosomal membrane proteins LAMP-I and LAMP-II (clustered on cell surface) and melanosomal membrane protein tyrosinase in fibroblasts and melanocytes, consistent with an alternate plasma-membrane trafficking pathway for AP-3 cargo. Homologous recombination knockout, compound heterozygote rescue, immunofluorescence localization of LAMP-I, LAMP-II, and tyrosinase Journal of cell science High 11058094
2002 Complete loss of AP3B1 (beta3A) protein due to nonsense mutations leads to co-depletion of the associated mu3 subunit of AP-3, and causes robust aberrant trafficking of LAMP-3 (a lysosomal membrane protein) to the plasma membrane instead of directly to the lysosome, demonstrating that AP3B1 is required for direct TGN-to-lysosome routing of integral lysosomal membrane proteins. Patient cell biology: immunoblotting for AP-3 subunits, immunofluorescence/cell-surface trafficking assay for LAMP-3 in fibroblasts from AP3B1-null patient Pediatric research High 11809908
2006 A homozygous genomic deletion causing in-frame skipping of exon 15 in AP3B1 perturbs AP-3 heterotetrameric complex assembly and causes aberrant trafficking of the transmembrane lysosomal protein CD63; in basal keratinocytes, incorporated immature melanosomes are rapidly degraded in large phagolysosomes. Genetic linkage analysis, targeted gene sequencing, immunofluorescence for CD63 trafficking, electron microscopy of keratinocytes Blood High 16537806
2009 AP3B1 (beta3A subunit of AP-3) is a substrate for IP7-mediated pyrophosphorylation on a prephosphorylated serine residue; Kif3A (a kinesin-superfamily motor protein) is identified as an AP3B1-binding partner, and IP7-mediated pyrophosphorylation of AP3B1 modulates its interaction with Kif3A, which in turn affects HIV-1 Gag release. IP7-mediated pyrophosphorylation assay in vitro, co-immunoprecipitation of AP3B1 and Kif3A, HIV-1 virus-like particle release assay with AP-3 complex perturbation Proceedings of the National Academy of Sciences of the United States of America Medium 19934039
2009 Loss-of-function mutations in AP3B1 cause defective cytotoxic T-lymphocyte (CTL) granule secretion (increased cell-surface CD63, reduced cytotoxicity) and platelet dense granule defects (impaired aggregation, reduced 3H-serotonin uptake), establishing AP3B1/AP-3 as required for biogenesis and/or function of secretory lysosomes in CTLs and platelet dense granules. Patient-derived CTL clones: CD63 surface expression assay, cytotoxicity assay; platelet aggregation and 3H-serotonin uptake assay Haematologica Medium 19679886
2004 A frameshift insertion in a homopolymeric adenine tract in exon 21 of the canine AP3B1 gene is the causative mutation in canine cyclic neutropenia; transcriptional slippage at this polyA tract generates both mutant and wild-type transcripts from homozygous mutant alleles, a consequence of transcriptional infidelity through homopolymeric sequences. RT-PCR subclone analysis of heterozygous and homozygous dogs, in vitro reporter assay for transcriptional slippage Nucleic acids research Medium 15576359
2014 In pearl (Ap3b1 mutant) eyes, hypopigmentation is more severe than in pale ear (Hps1 mutant) mice, total tyrosinase activity is higher (suggesting weaker degradation of aberrantly transported tyrosinase), and double heterozygous Hps1/Ap3b1 mice show iris hypopigmentation more severe than either single mutant, indicating that AP3B1 and HPS1 operate in distinct but synergistic pathways for ocular melanosome biogenesis and tyrosinase distribution. Comparative pigmentation analysis in single and double mutant mice, tyrosinase activity assay, histology Experimental eye research Medium 25160823
2019 AP3B1 mutation in pearl mice causes delayed testis development, reduced sperm count, and lower testosterone concentrations during spermatogenesis, and pe males show reduced lysosomes in Sertoli cells, establishing a role for AP3B1/AP-3 in male reproductive development distinct from HPS1. Comparative analysis of pe and ep mutant mice: sperm count, testosterone measurement, electron microscopy of sperm tails, litter size analysis Reproduction, fertility, and development Low 30786955
2024 AP3B1 interacts with PDIA3/ERP57 and is indispensable for PDIA3-triggered selective autophagy-mediated degradation of rabies virus G protein, thereby restricting RABV infection; AP3B1 was identified by affinity tag-purification mass spectrometry as a PDIA3 interactor and its requirement was confirmed by knockout experiments. Affinity tag-purification mass spectrometry, co-immunoprecipitation, AP3B1 knockout cell functional assay for RABV G protein degradation Autophagy Medium 39128851
2024 AP3B1 physically interacts with the SARS-CoV-2 envelope (E) protein in infected cells and acts as an antiviral factor: overexpression of AP3B1 suppresses SARS-CoV-2 replication, while siRNA-mediated depletion increases release of infectious virus, demonstrating an intrinsic antiviral barrier function of AP3B1. Immunoprecipitation and immunofluorescence in virus-infected cells, AP3B1 overexpression and siRNA knockdown with viral replication quantification Viruses Medium 39339853

Source papers

Stage 0 corpus · 23 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 The beta3A subunit gene (Ap3b1) of the AP-3 adaptor complex is altered in the mouse hypopigmentation mutant pearl, a model for Hermansky-Pudlak syndrome and night blindness. Human molecular genetics 214 9931340
2002 Nonsense mutations in ADTB3A cause complete deficiency of the beta3A subunit of adaptor complex-3 and severe Hermansky-Pudlak syndrome type 2. Pediatric research 119 11809908
2009 Inositol pyrophosphate mediated pyrophosphorylation of AP3B1 regulates HIV-1 Gag release. Proceedings of the National Academy of Sciences of the United States of America 114 19934039
2006 Identification of a homozygous deletion in the AP3B1 gene causing Hermansky-Pudlak syndrome, type 2. Blood 92 16537806
2000 Defective organellar membrane protein trafficking in Ap3b1-deficient cells. Journal of cell science 65 11058094
2009 Two patients with Hermansky Pudlak syndrome type 2 and novel mutations in AP3B1. Haematologica 43 19679886
2021 Germline variants in UNC13D and AP3B1 are enriched in COVID-19 patients experiencing severe cytokine storms. European journal of human genetics : EJHG 30 33867526
2013 Disruption of AP3B1 by a chromosome 5 inversion: a new disease mechanism in Hermansky-Pudlak syndrome type 2. BMC medical genetics 26 23557002
2000 Genomic structure of the mouse Ap3b1 gene in normal and pearl mice. Genomics 22 11056055
2015 Synergistic defects of UNC13D and AP3B1 leading to adult hemophagocytic lymphohistiocytosis. International journal of hematology 17 25980904
2004 Paradoxical homozygous expression from heterozygotes and heterozygous expression from homozygotes as a consequence of transcriptional infidelity through a polyadenine tract in the AP3B1 gene responsible for canine cyclic neutropenia. Nucleic acids research 14 15576359
2019 Novel AP3B1 compound heterozygous mutations in a Japanese patient with Hermansky-Pudlak syndrome type 2. The Journal of dermatology 10 31820501
2014 The Ap3b1 gene regulates the ocular melanosome biogenesis and tyrosinase distribution differently from the Hps1 gene. Experimental eye research 7 25160823
2020 The Mutation of the Ap3b1 Gene Causes Uterine Hypoplasia in Pearl Mice. Reproductive sciences (Thousand Oaks, Calif.) 6 32016796
2019 Different functions of biogenesis of lysosomal organelles complex 3 subunit 1 (Hps1) and adaptor-related protein complex 3, beta 1 subunit (Ap3b1) genes on spermatogenesis and male fertility. Reproduction, fertility, and development 6 30786955
2021 Generation and characterization of a control and patient-derived human iPSC line containing the Hermansky Pudlak type 2 (HPS2) associated heterozygous compound mutation in AP3B1. Stem cell research 3 34182253
2008 Sequence analysis of the SRGN, AP3B1, ARF6, and SH2D1A genes in familial hemophagocytic lymphohistiocytosis. Pediatric blood & cancer 3 18000860
2024 AP3B1 facilitates PDIA3/ERP57 function to regulate rabies virus glycoprotein selective degradation and viral entry. Autophagy 2 39128851
2024 AP3B1 Has Type I Interferon-Independent Antiviral Function against SARS-CoV-2. Viruses 2 39339853
2025 Canine Neuronal Ceroid Lipofuscinosis-like Disorder Associated with Sequence Variants in AP3B1 and TRAPPC9. Genes 1 41300827
2025 Synergistic blood-based diagnostic value of AP3B1 and BMPR2 in Parkinson's disease. NPJ Parkinson's disease 0 41152257
2022 Hemophagocytic Lymphohistiocytosis Associated with Synergistic Defects of AP3B1 and ATM Genes: A Case Report and Literature Review. Journal of clinical medicine 0 36614895
2020 Correction to: The Mutation of the Ap3b1 Gene Causes Uterine Hypoplasia in Pearl Mice. Reproductive sciences (Thousand Oaks, Calif.) 0 32016797

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