{"gene":"MCFD2","run_date":"2026-04-28T18:30:28","timeline":{"discoveries":[{"year":2005,"finding":"MCFD2 is retained in the endoplasmic reticulum through its interaction with LMAN1 (ERGIC-53), and endogenous LMAN1 and MCFD2 are present primarily in complex with each other at 1:1 stoichiometry. MCFD2 is not required for oligomerization of LMAN1. Both LMAN1 and MCFD2 interact specifically with coagulation factor VIII via its B domain through calcium-dependent protein-protein interactions, and the MCFD2-FVIII interaction is independent of LMAN1-MCFD2 complex formation.","method":"Co-immunoprecipitation, cross-linking-immunoprecipitation assay, Western blot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP with multiple orthogonal approaches, highly cited foundational paper","pmids":["15886209"],"is_preprint":false},{"year":2006,"finding":"In the absence of ERGIC-53 (LMAN1), MCFD2 is secreted rather than retained, confirming that LMAN1 is required for ER retention of MCFD2. Knockdown of MCFD2 has no effect on LMAN1 localization. MCFD2 is dispensable for the binding of cathepsin Z and cathepsin C to ERGIC-53, indicating MCFD2 specifically recruits coagulation factors V and VIII to the ERGIC-53 complex.","method":"siRNA knockdown, yellow fluorescent protein fragment complementation, immunofluorescence","journal":"Traffic (Copenhagen, Denmark)","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined localization and cargo-selectivity phenotype, replicated across multiple approaches","pmids":["17010120"],"is_preprint":false},{"year":2007,"finding":"The interaction of MCFD2 with ERGIC-53 (LMAN1) is calcium-dependent; at calcium concentrations below 0.2 mM the interaction becomes significantly weaker. MCFD2 binding to ERGIC-53 enhances the sugar-binding ability of ERGIC-53. Two disease-causing MCFD2 missense mutations show 3–4 orders of magnitude lower binding affinity for ERGIC-53.","method":"Surface plasmon resonance, flow cytometry with fluorescent ERGIC-53 probe, glycan-competition assay","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1 — quantitative in vitro binding assay (SPR) with multiple conditions and disease mutants","pmids":["18056485"],"is_preprint":false},{"year":2007,"finding":"Deletion of only 3 C-terminal residues (ΔS-L-Q) from MCFD2 impairs binding to ERGIC-53 due to modification of the 3D structure of MCFD2, establishing that the C-terminal integrity of MCFD2 is required for ERGIC-53 interaction.","method":"Biochemical binding assay, structural analysis of mutant","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 — functional mutation analysis with structural follow-up in a single lab","pmids":["17971482"],"is_preprint":false},{"year":2008,"finding":"The solution structure of human MCFD2 determined by NMR shows that MCFD2 is disordered in the apo (calcium-free) state and folds into a structured protein upon binding of Ca2+ to its two C-terminal EF-hand motifs, while retaining some N-terminal disorder. Disease-causing missense mutants are predominantly disordered even in the presence of calcium, explaining the calcium dependence of the MCFD2-ERGIC-53 interaction.","method":"NMR structure determination, circular dichroism spectroscopy of mutants","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional validation of disease mutants","pmids":["18590741"],"is_preprint":false},{"year":2009,"finding":"The C-terminal EF-hand domains of MCFD2 are both necessary and sufficient for interaction with LMAN1; deletion of the entire N-terminal non-EF-hand region does not affect LMAN1 binding. The EF-hand domains also mediate interaction with FV and FVIII, but mutations that abolish LMAN1 binding (and disrupt tertiary structure) still retain FV/FVIII binding, indicating the EF-hand domains contain separate binding sites for LMAN1 and for FV/FVIII.","method":"Deletion mutagenesis, co-immunoprecipitation, circular dichroism spectroscopy","journal":"Blood","confidence":"High","confidence_rationale":"Tier 1–2 — mutagenesis combined with CD spectroscopy and Co-IP, multiple orthogonal methods","pmids":["20007547"],"is_preprint":false},{"year":2010,"finding":"Crystal structure of the LMAN1-CRD/MCFD2 complex reveals that LMAN1 interacts with MCFD2 through its N-terminal beta sheet of the carbohydrate recognition domain (CRD). The CRD contains distinct, separable binding sites for MCFD2 and for cargo proteins (FV/FVIII): mutations in the first beta sheet abolish MCFD2 binding without affecting mannose binding, while mutations in the Ca2+- and sugar-binding sites disrupt FV/FVIII interaction without affecting MCFD2 binding. Monomeric LMAN1 mutants cannot exit the ER and cannot bind MCFD2, indicating oligomerization is required for cargo receptor function.","method":"Crystal structure, site-directed mutagenesis, co-immunoprecipitation","journal":"Blood / FEBS letters","confidence":"High","confidence_rationale":"Tier 1 — crystal structure combined with mutagenesis and co-IP, replicated across two independent studies","pmids":["20817851","20138881"],"is_preprint":false},{"year":2018,"finding":"MCFD2-deficient mice generated by gene targeting show reduced plasma FV and FVIII, with levels lower than in LMAN1-deficient mice. Doubly deficient (LMAN1/MCFD2 null) mice match the higher FV/FVIII levels of LMAN1-deficient mice, suggesting an alternative LMAN1-independent secretion pathway exists. LMAN1 and MCFD2 single deficiency also reduces plasma α1-antitrypsin (AAT) and causes AAT accumulation in hepatocyte ER, demonstrating a shared role in AAT ER exit.","method":"Gene targeting (knockout mice), plasma coagulation factor assays, hepatocyte ER fractionation","journal":"Blood advances","confidence":"High","confidence_rationale":"Tier 2 — clean KO mouse model with defined cargo-specific phenotypes and genetic epistasis","pmids":["29735583"],"is_preprint":false},{"year":2020,"finding":"Crystallographic snapshots of the ERGIC-53 CRD/MCFD2 complex at 1.60 Å resolution reveal that MCFD2 exhibits significant conformational plasticity whereas ERGIC-53-CRD does not, suggesting that MCFD2's structural flexibility underlies its ability to accommodate diverse polypeptide cargo ligands.","method":"X-ray crystallography (multiple crystal forms, 1.60 Å resolution)","journal":"Acta crystallographica. Section F, Structural biology communications","confidence":"Medium","confidence_rationale":"Tier 1 — crystal structure; functional interpretation is structural inference without direct mutagenesis of the proposed flexible surface","pmids":["32356523"],"is_preprint":false},{"year":2022,"finding":"LMAN1-MCFD2 is a cargo receptor for ER-to-Golgi transport of α1-antitrypsin (AAT). LMAN1 or MCFD2 knockout HepG2 and HEK293T cells show reduced AAT secretion and elevated intracellular AAT due to delayed ER-to-Golgi transport. Secretion defects are rescued by wild-type but not mutant LMAN1 or MCFD2. The interaction of LMAN1 with the second N-glycan of AAT is critical; loss of this glycosylation site abolishes LMAN1-dependent secretion. Co-IP in MCFD2 KO cells shows AAT interacts with LMAN1 independently of MCFD2.","method":"CRISPR/Cas9 knockout cells, secretion/chase assay, co-immunoprecipitation, glycosylation site mutagenesis","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods (KO rescue, Co-IP, glycan mutagenesis) in two cell lines","pmids":["35322856"],"is_preprint":false},{"year":2023,"finding":"Overexpression of wild-type or mutant MCFD2 alone is sufficient to rescue FV/FVIII secretion defects in LMAN1-deficient cells, indicating that MCFD2 carries out cargo binding and transport and that LMAN1 primarily serves as a shuttling carrier for MCFD2. LMAN1 carbohydrate-binding mutations only partially reduce FV/FVIII transport, indicating N-glycan binding is not essential for FV/FVIII cargo transport. Overexpression of both LMAN1 and MCFD2 does not further increase FV/FVIII secretion, indicating the complex is not rate-limiting.","method":"LMAN1/MCFD2 deficient cell lines, rescue overexpression experiments, coagulation factor secretion assays","journal":"Blood advances","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO cell lines with rescue assays; single lab, but uses multiple cell types and constructs","pmids":["36490287"],"is_preprint":false}],"current_model":"MCFD2 is a soluble, calcium-dependent EF-hand protein that folds upon Ca2+ binding and is retained in the ER lumen by a 1:1 interaction with the transmembrane lectin LMAN1 (ERGIC-53) via its EF-hand domains; together they form a cargo receptor complex that cycles between the ER and ERGIC to recruit coagulation factors V and VIII (via MCFD2's separate EF-hand cargo-binding site) and α1-antitrypsin (via LMAN1's lectin domain), mediating their efficient ER-to-Golgi transport, with LMAN1 acting primarily as the membrane shuttle and MCFD2 as the direct cargo-binding subunit."},"narrative":{"teleology":[{"year":2005,"claim":"Establishing MCFD2 as a stoichiometric partner of LMAN1 and demonstrating its direct, calcium-dependent interaction with FVIII resolved how combined FV/FVIII deficiency arises from mutations in two separate genes.","evidence":"Reciprocal co-immunoprecipitation and cross-linking in cell lysates","pmids":["15886209"],"confidence":"High","gaps":["Whether MCFD2 contributes to cargo selectivity beyond FV/FVIII was unknown","Structural basis of the MCFD2–LMAN1 interaction was unresolved","The calcium-dependence mechanism at the molecular level was not defined"]},{"year":2006,"claim":"Demonstrating that MCFD2 is secreted in the absence of LMAN1 and is dispensable for cathepsin cargo binding established that MCFD2 confers cargo selectivity for FV/FVIII rather than acting as a general co-receptor.","evidence":"siRNA knockdown of LMAN1/MCFD2 with immunofluorescence and cargo-binding assays","pmids":["17010120"],"confidence":"High","gaps":["Which domains of MCFD2 mediate cargo versus LMAN1 binding was unknown","In vivo relevance of MCFD2 loss had not been tested in an animal model"]},{"year":2008,"claim":"Solving the NMR structure of MCFD2 revealed that it is intrinsically disordered without calcium and folds upon Ca²⁺ binding to its EF-hands, explaining why the MCFD2–LMAN1 interaction is calcium-dependent and why disease mutations cause structural disorder.","evidence":"NMR structure determination and circular dichroism of wild-type and disease mutants","pmids":["18590741"],"confidence":"High","gaps":["The atomic details of the MCFD2–LMAN1 interface were still unknown","Whether the disordered N-terminal region has any functional role was unresolved"]},{"year":2009,"claim":"Mapping the EF-hand domains as both necessary and sufficient for LMAN1 and FV/FVIII binding — yet showing these are separable sites — established that MCFD2 simultaneously engages its receptor and its cargo through distinct surfaces.","evidence":"Deletion mutagenesis combined with co-immunoprecipitation and CD spectroscopy","pmids":["20007547"],"confidence":"High","gaps":["The structural basis of the cargo-binding site on MCFD2 was not resolved","Whether conformational flexibility of MCFD2 contributes to cargo recognition was speculative"]},{"year":2010,"claim":"Crystal structures of the LMAN1-CRD/MCFD2 complex defined the binding interface on the N-terminal β-sheet of the LMAN1 CRD, distinct from its sugar-binding site, and showed that LMAN1 oligomerization is required for ER exit and cargo receptor function.","evidence":"X-ray crystallography combined with site-directed mutagenesis and co-immunoprecipitation","pmids":["20817851","20138881"],"confidence":"High","gaps":["No structure of MCFD2 bound to FV or FVIII cargo was available","Mechanism by which oligomerization enables ER exit was not determined"]},{"year":2018,"claim":"MCFD2-knockout mice confirmed the in vivo requirement for FV/FVIII secretion and extended the cargo repertoire to α1-antitrypsin; epistasis with LMAN1 knockout revealed an alternative LMAN1-independent secretion pathway.","evidence":"Gene-targeted single and double knockout mice with plasma factor assays and hepatocyte ER fractionation","pmids":["29735583"],"confidence":"High","gaps":["Identity of the alternative LMAN1-independent secretion pathway was unknown","Whether additional cargo proteins depend on MCFD2 in vivo was not surveyed"]},{"year":2020,"claim":"High-resolution crystallographic snapshots revealed conformational plasticity of MCFD2 within the complex, suggesting this flexibility enables accommodation of diverse cargo ligands.","evidence":"Multiple crystal forms of the ERGIC-53 CRD/MCFD2 complex at 1.60 Å resolution","pmids":["32356523"],"confidence":"Medium","gaps":["No direct mutagenesis of the proposed flexible cargo-binding surface was performed","Whether conformational plasticity is functionally required for cargo binding was not tested"]},{"year":2022,"claim":"Demonstrating that LMAN1–MCFD2 is a cargo receptor for α1-antitrypsin via the second N-glycan of AAT, while AAT binds LMAN1 independently of MCFD2, defined a glycan-dependent transport mode distinct from the MCFD2-dependent FV/FVIII pathway.","evidence":"CRISPR knockout and rescue in HepG2 and HEK293T cells, glycosylation site mutagenesis, co-immunoprecipitation","pmids":["35322856"],"confidence":"High","gaps":["Whether MCFD2 contributes to AAT binding cooperativity with LMAN1 or is merely a co-factor for ER exit was unclear","The full repertoire of LMAN1-dependent versus MCFD2-dependent cargo was not defined"]},{"year":2023,"claim":"Showing that MCFD2 overexpression alone rescues FV/FVIII secretion in LMAN1-null cells redefined MCFD2 as the primary cargo-binding and transport subunit, with LMAN1 serving as a membrane shuttle rather than a co-receptor.","evidence":"Rescue overexpression in LMAN1/MCFD2-deficient cell lines with FV/FVIII secretion assays","pmids":["36490287"],"confidence":"Medium","gaps":["How MCFD2 exits the ER without LMAN1 when overexpressed was not mechanistically resolved","Single-lab finding; independent confirmation is needed","Whether endogenous-level MCFD2 can function without LMAN1 in vivo was not tested"]},{"year":null,"claim":"The structural basis of MCFD2's direct interaction with FV/FVIII cargo and the mechanism by which MCFD2 can mediate ER exit independently of LMAN1 remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structure of MCFD2 in complex with FV or FVIII has been determined","The alternative LMAN1-independent export mechanism is uncharacterized","A comprehensive cargo proteome for MCFD2 has not been defined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0038024","term_label":"cargo receptor activity","supporting_discovery_ids":[0,1,5,10]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,5,6]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[0,1]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[1]}],"pathway":[{"term_id":"R-HSA-9609507","term_label":"Protein localization","supporting_discovery_ids":[0,1,7,9,10]},{"term_id":"R-HSA-5653656","term_label":"Vesicle-mediated transport","supporting_discovery_ids":[1,7,9]},{"term_id":"R-HSA-109582","term_label":"Hemostasis","supporting_discovery_ids":[0,7,10]}],"complexes":["LMAN1–MCFD2 cargo receptor complex"],"partners":["LMAN1","F5","F8","SERPINA1"],"other_free_text":[]},"mechanistic_narrative":"MCFD2 is a soluble, calcium-dependent EF-hand protein that functions as the direct cargo-binding subunit of the LMAN1(ERGIC-53)–MCFD2 cargo receptor complex, mediating ER-to-Golgi transport of coagulation factors V and VIII and α1-antitrypsin. MCFD2 is intrinsically disordered in the absence of calcium and folds upon Ca²⁺ binding to its two C-terminal EF-hand motifs, which contain separable binding sites for LMAN1 and for FV/FVIII cargo [PMID:18590741, PMID:20007547]. LMAN1 retains MCFD2 in the early secretory pathway and serves primarily as a membrane shuttle, while MCFD2 is the cargo-selective subunit: it is dispensable for cathepsin recruitment but essential for efficient FV/FVIII secretion, and overexpression of MCFD2 alone can rescue FV/FVIII export even in LMAN1-deficient cells [PMID:17010120, PMID:36490287]. Knockout mice lacking MCFD2 exhibit reduced plasma FV, FVIII, and α1-antitrypsin levels, with hepatocyte ER accumulation of α1-antitrypsin confirming a physiological role in secretory cargo export [PMID:29735583]."},"prefetch_data":{"uniprot":{"accession":"Q8NI22","full_name":"Multiple coagulation factor deficiency protein 2","aliases":["Neural stem cell-derived neuronal survival protein"],"length_aa":146,"mass_kda":16.4,"function":"The MCFD2-LMAN1 complex forms a specific cargo receptor for the ER-to-Golgi transport of selected proteins. Plays a role in the secretion of coagulation factors","subcellular_location":"Endoplasmic reticulum-Golgi intermediate compartment; Endoplasmic reticulum; Golgi apparatus","url":"https://www.uniprot.org/uniprotkb/Q8NI22/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/MCFD2","classification":"Not Classified","n_dependent_lines":3,"n_total_lines":1208,"dependency_fraction":0.0024834437086092716},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"LMAN1","stoichiometry":10.0},{"gene":"COPA","stoichiometry":0.2},{"gene":"COPE","stoichiometry":0.2},{"gene":"SEC13","stoichiometry":0.2},{"gene":"YIPF5","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/MCFD2","total_profiled":1310},"omim":[{"mim_id":"613625","title":"FACTOR V AND FACTOR VIII, COMBINED DEFICIENCY OF, 2; F5F8D2","url":"https://www.omim.org/entry/613625"},{"mim_id":"607788","title":"MULTIPLE COAGULATION FACTOR DEFICIENCY PROTEIN 2; MCFD2","url":"https://www.omim.org/entry/607788"},{"mim_id":"601567","title":"LECTIN, MANNOSE-BINDING 1; LMAN1","url":"https://www.omim.org/entry/601567"},{"mim_id":"227300","title":"FACTOR V AND FACTOR VIII, COMBINED DEFICIENCY OF, 1; F5F8D1","url":"https://www.omim.org/entry/227300"},{"mim_id":"134510","title":"FACTOR VIII AND FACTOR IX, COMBINED DEFICIENCY OF; F8F9D","url":"https://www.omim.org/entry/134510"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"","locations":[],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/MCFD2"},"hgnc":{"alias_symbol":["F5F8D","LMAN1IP","SDNSF"],"prev_symbol":[]},"alphafold":{"accession":"Q8NI22","domains":[{"cath_id":"1.10.238.10","chopping":"68-144","consensus_level":"high","plddt":89.95,"start":68,"end":144}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NI22","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NI22-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NI22-F1-predicted_aligned_error_v6.png","plddt_mean":76.19},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=MCFD2","jax_strain_url":"https://www.jax.org/strain/search?query=MCFD2"},"sequence":{"accession":"Q8NI22","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NI22.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NI22/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NI22"}},"corpus_meta":[{"pmid":"15886209","id":"PMC_15886209","title":"LMAN1 and MCFD2 form a cargo receptor complex and interact with coagulation factor VIII in the early secretory pathway.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15886209","citation_count":113,"is_preprint":false},{"pmid":"16304051","id":"PMC_16304051","title":"Combined deficiency of factor V and factor VIII is due to mutations in either LMAN1 or MCFD2.","date":"2005","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/16304051","citation_count":86,"is_preprint":false},{"pmid":"17010120","id":"PMC_17010120","title":"Cargo selectivity of the ERGIC-53/MCFD2 transport receptor complex.","date":"2006","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/17010120","citation_count":65,"is_preprint":false},{"pmid":"20817851","id":"PMC_20817851","title":"Molecular basis of LMAN1 in coordinating LMAN1-MCFD2 cargo receptor formation and ER-to-Golgi transport of FV/FVIII.","date":"2010","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20817851","citation_count":50,"is_preprint":false},{"pmid":"18056485","id":"PMC_18056485","title":"The sugar-binding ability of ERGIC-53 is enhanced by its interaction with MCFD2.","date":"2007","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/18056485","citation_count":46,"is_preprint":false},{"pmid":"9245995","id":"PMC_9245995","title":"The locus for combined factor V-factor VIII deficiency (F5F8D) maps to 18q21, between D18S849 and D18S1103.","date":"1997","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/9245995","citation_count":36,"is_preprint":false},{"pmid":"18590741","id":"PMC_18590741","title":"New insights into multiple coagulation factor deficiency from the solution structure of human MCFD2.","date":"2008","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18590741","citation_count":30,"is_preprint":false},{"pmid":"20007547","id":"PMC_20007547","title":"EF-hand domains of MCFD2 mediate interactions with both LMAN1 and coagulation factor V or VIII.","date":"2009","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/20007547","citation_count":23,"is_preprint":false},{"pmid":"20138881","id":"PMC_20138881","title":"Crystal structure of the LMAN1-CRD/MCFD2 transport receptor complex provides insight into combined deficiency of factor V and factor VIII.","date":"2010","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/20138881","citation_count":22,"is_preprint":false},{"pmid":"17971482","id":"PMC_17971482","title":"Deletion of 3 residues from the C-terminus of MCFD2 affects binding to ERGIC-53 and causes combined factor V and factor VIII deficiency.","date":"2007","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/17971482","citation_count":20,"is_preprint":false},{"pmid":"16044454","id":"PMC_16044454","title":"Mutations in the MCFD2 gene and a novel mutation in the LMAN1 gene in Indian families with combined deficiency of factor V and VIII.","date":"2005","source":"American journal of hematology","url":"https://pubmed.ncbi.nlm.nih.gov/16044454","citation_count":20,"is_preprint":false},{"pmid":"29735583","id":"PMC_29735583","title":"Analysis of MCFD2- and LMAN1-deficient mice demonstrates distinct functions in vivo.","date":"2018","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/29735583","citation_count":19,"is_preprint":false},{"pmid":"35322856","id":"PMC_35322856","title":"LMAN1-MCFD2 complex is a cargo receptor for the ER-Golgi transport of α1-antitrypsin.","date":"2022","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/35322856","citation_count":16,"is_preprint":false},{"pmid":"17610559","id":"PMC_17610559","title":"Mutations in the MCFD2 gene are predominant among patients with hereditary combined FV and FVIII deficiency (F5F8D) in India.","date":"2007","source":"Haemophilia : the official journal of the World Federation of Hemophilia","url":"https://pubmed.ncbi.nlm.nih.gov/17610559","citation_count":14,"is_preprint":false},{"pmid":"21492322","id":"PMC_21492322","title":"Analysis of newly detected mutations in the MCFD2 gene giving rise to combined deficiency of coagulation factors V and VIII.","date":"2011","source":"Haemophilia : the official journal of the World Federation of Hemophilia","url":"https://pubmed.ncbi.nlm.nih.gov/21492322","citation_count":12,"is_preprint":false},{"pmid":"36490287","id":"PMC_36490287","title":"Separate roles of LMAN1 and MCFD2 in ER-to-Golgi trafficking of FV and FVIII.","date":"2023","source":"Blood advances","url":"https://pubmed.ncbi.nlm.nih.gov/36490287","citation_count":10,"is_preprint":false},{"pmid":"32356523","id":"PMC_32356523","title":"Crystallographic snapshots of the EF-hand protein MCFD2 complexed with the intracellular lectin ERGIC-53 involved in glycoprotein transport.","date":"2020","source":"Acta crystallographica. Section F, Structural biology communications","url":"https://pubmed.ncbi.nlm.nih.gov/32356523","citation_count":8,"is_preprint":false},{"pmid":"35963666","id":"PMC_35963666","title":"Effect of co-overexpression of the cargo receptor ERGIC-53/MCFD2 on antibody production and intracellular IgG secretion in recombinant Chinese hamster ovary cells.","date":"2022","source":"Journal of bioscience and bioengineering","url":"https://pubmed.ncbi.nlm.nih.gov/35963666","citation_count":8,"is_preprint":false},{"pmid":"18685427","id":"PMC_18685427","title":"The first case of combined coagulation factor V and coagulation factor VIII deficiency in Poland due to a novel p.Tyr135Asn missense mutation in the MCFD2 gene.","date":"2008","source":"Blood coagulation & fibrinolysis : an international journal in haemostasis and thrombosis","url":"https://pubmed.ncbi.nlm.nih.gov/18685427","citation_count":8,"is_preprint":false},{"pmid":"22208273","id":"PMC_22208273","title":"Unveiling the unfolding pathway of F5F8D disorder-associated D81H/V100D mutant of MCFD2 via multiple molecular dynamics simulations.","date":"2012","source":"Journal of biomolecular structure & dynamics","url":"https://pubmed.ncbi.nlm.nih.gov/22208273","citation_count":5,"is_preprint":false},{"pmid":"39222205","id":"PMC_39222205","title":"RNAi targeting LMAN1-MCFD2 complex promotes anticoagulation in mice.","date":"2024","source":"Journal of thrombosis and thrombolysis","url":"https://pubmed.ncbi.nlm.nih.gov/39222205","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11556,"output_tokens":2989,"usd":0.039752},"stage2":{"model":"claude-opus-4-6","input_tokens":6338,"output_tokens":2614,"usd":0.14556},"total_usd":0.185312,"stage1_batch_id":"msgbatch_01Mgbec4vM6c9vXht7JVJzss","stage2_batch_id":"msgbatch_01JkuuH5RB2BdJNsgnhjbC6s","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"MCFD2 is retained in the endoplasmic reticulum through its interaction with LMAN1 (ERGIC-53), and endogenous LMAN1 and MCFD2 are present primarily in complex with each other at 1:1 stoichiometry. MCFD2 is not required for oligomerization of LMAN1. Both LMAN1 and MCFD2 interact specifically with coagulation factor VIII via its B domain through calcium-dependent protein-protein interactions, and the MCFD2-FVIII interaction is independent of LMAN1-MCFD2 complex formation.\",\n      \"method\": \"Co-immunoprecipitation, cross-linking-immunoprecipitation assay, Western blot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP with multiple orthogonal approaches, highly cited foundational paper\",\n      \"pmids\": [\"15886209\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In the absence of ERGIC-53 (LMAN1), MCFD2 is secreted rather than retained, confirming that LMAN1 is required for ER retention of MCFD2. Knockdown of MCFD2 has no effect on LMAN1 localization. MCFD2 is dispensable for the binding of cathepsin Z and cathepsin C to ERGIC-53, indicating MCFD2 specifically recruits coagulation factors V and VIII to the ERGIC-53 complex.\",\n      \"method\": \"siRNA knockdown, yellow fluorescent protein fragment complementation, immunofluorescence\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined localization and cargo-selectivity phenotype, replicated across multiple approaches\",\n      \"pmids\": [\"17010120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The interaction of MCFD2 with ERGIC-53 (LMAN1) is calcium-dependent; at calcium concentrations below 0.2 mM the interaction becomes significantly weaker. MCFD2 binding to ERGIC-53 enhances the sugar-binding ability of ERGIC-53. Two disease-causing MCFD2 missense mutations show 3–4 orders of magnitude lower binding affinity for ERGIC-53.\",\n      \"method\": \"Surface plasmon resonance, flow cytometry with fluorescent ERGIC-53 probe, glycan-competition assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — quantitative in vitro binding assay (SPR) with multiple conditions and disease mutants\",\n      \"pmids\": [\"18056485\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Deletion of only 3 C-terminal residues (ΔS-L-Q) from MCFD2 impairs binding to ERGIC-53 due to modification of the 3D structure of MCFD2, establishing that the C-terminal integrity of MCFD2 is required for ERGIC-53 interaction.\",\n      \"method\": \"Biochemical binding assay, structural analysis of mutant\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — functional mutation analysis with structural follow-up in a single lab\",\n      \"pmids\": [\"17971482\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The solution structure of human MCFD2 determined by NMR shows that MCFD2 is disordered in the apo (calcium-free) state and folds into a structured protein upon binding of Ca2+ to its two C-terminal EF-hand motifs, while retaining some N-terminal disorder. Disease-causing missense mutants are predominantly disordered even in the presence of calcium, explaining the calcium dependence of the MCFD2-ERGIC-53 interaction.\",\n      \"method\": \"NMR structure determination, circular dichroism spectroscopy of mutants\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional validation of disease mutants\",\n      \"pmids\": [\"18590741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The C-terminal EF-hand domains of MCFD2 are both necessary and sufficient for interaction with LMAN1; deletion of the entire N-terminal non-EF-hand region does not affect LMAN1 binding. The EF-hand domains also mediate interaction with FV and FVIII, but mutations that abolish LMAN1 binding (and disrupt tertiary structure) still retain FV/FVIII binding, indicating the EF-hand domains contain separate binding sites for LMAN1 and for FV/FVIII.\",\n      \"method\": \"Deletion mutagenesis, co-immunoprecipitation, circular dichroism spectroscopy\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 — mutagenesis combined with CD spectroscopy and Co-IP, multiple orthogonal methods\",\n      \"pmids\": [\"20007547\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Crystal structure of the LMAN1-CRD/MCFD2 complex reveals that LMAN1 interacts with MCFD2 through its N-terminal beta sheet of the carbohydrate recognition domain (CRD). The CRD contains distinct, separable binding sites for MCFD2 and for cargo proteins (FV/FVIII): mutations in the first beta sheet abolish MCFD2 binding without affecting mannose binding, while mutations in the Ca2+- and sugar-binding sites disrupt FV/FVIII interaction without affecting MCFD2 binding. Monomeric LMAN1 mutants cannot exit the ER and cannot bind MCFD2, indicating oligomerization is required for cargo receptor function.\",\n      \"method\": \"Crystal structure, site-directed mutagenesis, co-immunoprecipitation\",\n      \"journal\": \"Blood / FEBS letters\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure combined with mutagenesis and co-IP, replicated across two independent studies\",\n      \"pmids\": [\"20817851\", \"20138881\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"MCFD2-deficient mice generated by gene targeting show reduced plasma FV and FVIII, with levels lower than in LMAN1-deficient mice. Doubly deficient (LMAN1/MCFD2 null) mice match the higher FV/FVIII levels of LMAN1-deficient mice, suggesting an alternative LMAN1-independent secretion pathway exists. LMAN1 and MCFD2 single deficiency also reduces plasma α1-antitrypsin (AAT) and causes AAT accumulation in hepatocyte ER, demonstrating a shared role in AAT ER exit.\",\n      \"method\": \"Gene targeting (knockout mice), plasma coagulation factor assays, hepatocyte ER fractionation\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KO mouse model with defined cargo-specific phenotypes and genetic epistasis\",\n      \"pmids\": [\"29735583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystallographic snapshots of the ERGIC-53 CRD/MCFD2 complex at 1.60 Å resolution reveal that MCFD2 exhibits significant conformational plasticity whereas ERGIC-53-CRD does not, suggesting that MCFD2's structural flexibility underlies its ability to accommodate diverse polypeptide cargo ligands.\",\n      \"method\": \"X-ray crystallography (multiple crystal forms, 1.60 Å resolution)\",\n      \"journal\": \"Acta crystallographica. Section F, Structural biology communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure; functional interpretation is structural inference without direct mutagenesis of the proposed flexible surface\",\n      \"pmids\": [\"32356523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"LMAN1-MCFD2 is a cargo receptor for ER-to-Golgi transport of α1-antitrypsin (AAT). LMAN1 or MCFD2 knockout HepG2 and HEK293T cells show reduced AAT secretion and elevated intracellular AAT due to delayed ER-to-Golgi transport. Secretion defects are rescued by wild-type but not mutant LMAN1 or MCFD2. The interaction of LMAN1 with the second N-glycan of AAT is critical; loss of this glycosylation site abolishes LMAN1-dependent secretion. Co-IP in MCFD2 KO cells shows AAT interacts with LMAN1 independently of MCFD2.\",\n      \"method\": \"CRISPR/Cas9 knockout cells, secretion/chase assay, co-immunoprecipitation, glycosylation site mutagenesis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods (KO rescue, Co-IP, glycan mutagenesis) in two cell lines\",\n      \"pmids\": [\"35322856\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Overexpression of wild-type or mutant MCFD2 alone is sufficient to rescue FV/FVIII secretion defects in LMAN1-deficient cells, indicating that MCFD2 carries out cargo binding and transport and that LMAN1 primarily serves as a shuttling carrier for MCFD2. LMAN1 carbohydrate-binding mutations only partially reduce FV/FVIII transport, indicating N-glycan binding is not essential for FV/FVIII cargo transport. Overexpression of both LMAN1 and MCFD2 does not further increase FV/FVIII secretion, indicating the complex is not rate-limiting.\",\n      \"method\": \"LMAN1/MCFD2 deficient cell lines, rescue overexpression experiments, coagulation factor secretion assays\",\n      \"journal\": \"Blood advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO cell lines with rescue assays; single lab, but uses multiple cell types and constructs\",\n      \"pmids\": [\"36490287\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"MCFD2 is a soluble, calcium-dependent EF-hand protein that folds upon Ca2+ binding and is retained in the ER lumen by a 1:1 interaction with the transmembrane lectin LMAN1 (ERGIC-53) via its EF-hand domains; together they form a cargo receptor complex that cycles between the ER and ERGIC to recruit coagulation factors V and VIII (via MCFD2's separate EF-hand cargo-binding site) and α1-antitrypsin (via LMAN1's lectin domain), mediating their efficient ER-to-Golgi transport, with LMAN1 acting primarily as the membrane shuttle and MCFD2 as the direct cargo-binding subunit.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"MCFD2 is a soluble, calcium-dependent EF-hand protein that functions as the direct cargo-binding subunit of the LMAN1(ERGIC-53)–MCFD2 cargo receptor complex, mediating ER-to-Golgi transport of coagulation factors V and VIII and α1-antitrypsin. MCFD2 is intrinsically disordered in the absence of calcium and folds upon Ca²⁺ binding to its two C-terminal EF-hand motifs, which contain separable binding sites for LMAN1 and for FV/FVIII cargo [PMID:18590741, PMID:20007547]. LMAN1 retains MCFD2 in the early secretory pathway and serves primarily as a membrane shuttle, while MCFD2 is the cargo-selective subunit: it is dispensable for cathepsin recruitment but essential for efficient FV/FVIII secretion, and overexpression of MCFD2 alone can rescue FV/FVIII export even in LMAN1-deficient cells [PMID:17010120, PMID:36490287]. Knockout mice lacking MCFD2 exhibit reduced plasma FV, FVIII, and α1-antitrypsin levels, with hepatocyte ER accumulation of α1-antitrypsin confirming a physiological role in secretory cargo export [PMID:29735583].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"Establishing MCFD2 as a stoichiometric partner of LMAN1 and demonstrating its direct, calcium-dependent interaction with FVIII resolved how combined FV/FVIII deficiency arises from mutations in two separate genes.\",\n      \"evidence\": \"Reciprocal co-immunoprecipitation and cross-linking in cell lysates\",\n      \"pmids\": [\"15886209\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether MCFD2 contributes to cargo selectivity beyond FV/FVIII was unknown\",\n        \"Structural basis of the MCFD2–LMAN1 interaction was unresolved\",\n        \"The calcium-dependence mechanism at the molecular level was not defined\"\n      ]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrating that MCFD2 is secreted in the absence of LMAN1 and is dispensable for cathepsin cargo binding established that MCFD2 confers cargo selectivity for FV/FVIII rather than acting as a general co-receptor.\",\n      \"evidence\": \"siRNA knockdown of LMAN1/MCFD2 with immunofluorescence and cargo-binding assays\",\n      \"pmids\": [\"17010120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Which domains of MCFD2 mediate cargo versus LMAN1 binding was unknown\",\n        \"In vivo relevance of MCFD2 loss had not been tested in an animal model\"\n      ]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Solving the NMR structure of MCFD2 revealed that it is intrinsically disordered without calcium and folds upon Ca²⁺ binding to its EF-hands, explaining why the MCFD2–LMAN1 interaction is calcium-dependent and why disease mutations cause structural disorder.\",\n      \"evidence\": \"NMR structure determination and circular dichroism of wild-type and disease mutants\",\n      \"pmids\": [\"18590741\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The atomic details of the MCFD2–LMAN1 interface were still unknown\",\n        \"Whether the disordered N-terminal region has any functional role was unresolved\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Mapping the EF-hand domains as both necessary and sufficient for LMAN1 and FV/FVIII binding — yet showing these are separable sites — established that MCFD2 simultaneously engages its receptor and its cargo through distinct surfaces.\",\n      \"evidence\": \"Deletion mutagenesis combined with co-immunoprecipitation and CD spectroscopy\",\n      \"pmids\": [\"20007547\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"The structural basis of the cargo-binding site on MCFD2 was not resolved\",\n        \"Whether conformational flexibility of MCFD2 contributes to cargo recognition was speculative\"\n      ]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Crystal structures of the LMAN1-CRD/MCFD2 complex defined the binding interface on the N-terminal β-sheet of the LMAN1 CRD, distinct from its sugar-binding site, and showed that LMAN1 oligomerization is required for ER exit and cargo receptor function.\",\n      \"evidence\": \"X-ray crystallography combined with site-directed mutagenesis and co-immunoprecipitation\",\n      \"pmids\": [\"20817851\", \"20138881\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"No structure of MCFD2 bound to FV or FVIII cargo was available\",\n        \"Mechanism by which oligomerization enables ER exit was not determined\"\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"MCFD2-knockout mice confirmed the in vivo requirement for FV/FVIII secretion and extended the cargo repertoire to α1-antitrypsin; epistasis with LMAN1 knockout revealed an alternative LMAN1-independent secretion pathway.\",\n      \"evidence\": \"Gene-targeted single and double knockout mice with plasma factor assays and hepatocyte ER fractionation\",\n      \"pmids\": [\"29735583\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Identity of the alternative LMAN1-independent secretion pathway was unknown\",\n        \"Whether additional cargo proteins depend on MCFD2 in vivo was not surveyed\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"High-resolution crystallographic snapshots revealed conformational plasticity of MCFD2 within the complex, suggesting this flexibility enables accommodation of diverse cargo ligands.\",\n      \"evidence\": \"Multiple crystal forms of the ERGIC-53 CRD/MCFD2 complex at 1.60 Å resolution\",\n      \"pmids\": [\"32356523\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No direct mutagenesis of the proposed flexible cargo-binding surface was performed\",\n        \"Whether conformational plasticity is functionally required for cargo binding was not tested\"\n      ]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrating that LMAN1–MCFD2 is a cargo receptor for α1-antitrypsin via the second N-glycan of AAT, while AAT binds LMAN1 independently of MCFD2, defined a glycan-dependent transport mode distinct from the MCFD2-dependent FV/FVIII pathway.\",\n      \"evidence\": \"CRISPR knockout and rescue in HepG2 and HEK293T cells, glycosylation site mutagenesis, co-immunoprecipitation\",\n      \"pmids\": [\"35322856\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether MCFD2 contributes to AAT binding cooperativity with LMAN1 or is merely a co-factor for ER exit was unclear\",\n        \"The full repertoire of LMAN1-dependent versus MCFD2-dependent cargo was not defined\"\n      ]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showing that MCFD2 overexpression alone rescues FV/FVIII secretion in LMAN1-null cells redefined MCFD2 as the primary cargo-binding and transport subunit, with LMAN1 serving as a membrane shuttle rather than a co-receptor.\",\n      \"evidence\": \"Rescue overexpression in LMAN1/MCFD2-deficient cell lines with FV/FVIII secretion assays\",\n      \"pmids\": [\"36490287\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"How MCFD2 exits the ER without LMAN1 when overexpressed was not mechanistically resolved\",\n        \"Single-lab finding; independent confirmation is needed\",\n        \"Whether endogenous-level MCFD2 can function without LMAN1 in vivo was not tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The structural basis of MCFD2's direct interaction with FV/FVIII cargo and the mechanism by which MCFD2 can mediate ER exit independently of LMAN1 remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No structure of MCFD2 in complex with FV or FVIII has been determined\",\n        \"The alternative LMAN1-independent export mechanism is uncharacterized\",\n        \"A comprehensive cargo proteome for MCFD2 has not been defined\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [0, 1, 5, 10]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [0, 1]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-9609507\", \"supporting_discovery_ids\": [0, 1, 7, 9, 10]},\n      {\"term_id\": \"R-HSA-5653656\", \"supporting_discovery_ids\": [1, 7, 9]},\n      {\"term_id\": \"R-HSA-109582\", \"supporting_discovery_ids\": [0, 7, 10]}\n    ],\n    \"complexes\": [\n      \"LMAN1–MCFD2 cargo receptor complex\"\n    ],\n    \"partners\": [\n      \"LMAN1\",\n      \"F5\",\n      \"F8\",\n      \"SERPINA1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}