Affinage

AP3B1

AP-3 complex subunit beta-1 · UniProt O00203

Length
1094 aa
Mass
121.3 kDa
Annotated
2026-04-28
27 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

AP3B1 encodes the β3A subunit of the heterotetrameric AP-3 adaptor complex, which mediates vesicular trafficking of transmembrane cargo proteins from the trans-Golgi network and endosomes to lysosomes, melanosomes, and platelet dense granules (PMID:9931340, PMID:11058094). Loss of AP3B1 destabilizes the AP-3 complex (including co-depletion of the μ3 subunit), causing mislocalization of lysosomal membrane proteins (LAMP-1, LAMP-2, CD63) and melanosomal proteins (tyrosinase) to the plasma membrane, and impairs cytotoxic T lymphocyte degranulation, neutrophil granule sorting, and platelet dense granule function (PMID:11809908, PMID:16537806, PMID:19679886, PMID:38238087). Biallelic loss-of-function mutations in AP3B1 cause Hermansky–Pudlak syndrome type 2 (HPS2), characterized by oculocutaneous albinism, bleeding diathesis, immunodeficiency, and neutropenia (PMID:11809908, PMID:16537806). AP3B1 is also a substrate for IP7-mediated pyrophosphorylation that regulates its interaction with the kinesin motor Kif3A, and it participates in antiviral defense by restricting SARS-CoV-2 replication via interaction with the viral envelope protein and by enabling PDIA3-triggered selective autophagy of rabies virus G protein (PMID:19934039, PMID:39339853, PMID:39128851).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 1999 High

    Positional cloning of the pearl mouse locus established that AP3B1 encodes the β3A subunit of AP-3 and that its disruption causes combined defects in lysosomes, melanosomes, and platelet dense granules, defining AP-3 as a shared sorting machinery for lysosome-related organelles.

    Evidence Positional/candidate cloning with identification of tandem duplication and deletion mutations in pearl alleles

    PMID:9931340

    Open questions at the time
    • Specific cargo recognized by AP-3 not yet identified
    • Mechanism of AP-3 recruitment to membranes unknown
  2. 2000 High

    Knockout studies revealed that AP3B1 loss causes specific mislocalization of LAMP-I, LAMP-II, and tyrosinase to the cell surface rather than lysosomes/melanosomes, demonstrating that AP-3 mediates an intracellular sorting route that bypasses the plasma membrane.

    Evidence Ap3b1 homologous recombination knockout mice; immunofluorescence in fibroblasts and melanocytes

    PMID:11058094

    Open questions at the time
    • Sorting signals on cargo proteins recognized by AP-3 not mapped
    • Whether AP-3 acts at TGN versus endosomes not resolved
  3. 2002 High

    Human patient mutations and genetic epistasis in mice established that AP3B1 is essential for AP-3 complex integrity (co-depletion of μ3 subunit), that CD63 mistrafficking is a hallmark of AP3B1 deficiency, and that AP3B1/HPS2 acts in a pathway parallel to HPS1 for lysosome-related organelle biogenesis.

    Evidence Patient nonsense mutations with immunoblotting for subunit levels and CD63 trafficking assays; double mutant (pearl × pale ear) mouse phenotyping

    PMID:11809908 PMID:11861280

    Open questions at the time
    • Structural basis of β3A interaction with other AP-3 subunits not determined
    • How HPS1 and AP3B1 pathways converge on organelle biogenesis not defined
  4. 2006 High

    Identification of an in-frame exon-skipping mutation showed that even partial disruption of AP3B1 perturbs AP-3 assembly sufficiently to cause CD63 mistrafficking, melanosome degradation in keratinocytes, and reduced NK/NKT cell numbers, extending AP-3's role to immune cell homeostasis.

    Evidence Genetic linkage, gene sequencing, CD63 trafficking assay, electron microscopy, and immunological phenotyping in HPS2 patient

    PMID:16537806

    Open questions at the time
    • Mechanism of NK/NKT cell reduction not elucidated
    • Whether immune defects are cell-autonomous not tested
  5. 2009 High

    Discovery that AP3B1 is pyrophosphorylated by IP7 on a prephosphorylated serine, modulating its interaction with the kinesin motor Kif3A, revealed a post-translational regulatory mechanism linking inositol pyrophosphate signaling to AP-3-dependent vesicular transport.

    Evidence In vitro pyrophosphorylation assay, co-immunoprecipitation identifying Kif3A, and HIV-1 Gag release assay

    PMID:19934039

    Open questions at the time
    • Identity of the pyrophosphorylated serine residue not mapped in vivo
    • Physiological consequence of IP7-mediated regulation on endogenous cargo trafficking not tested
  6. 2009 Medium

    Patient-derived CTL and platelet studies demonstrated that AP3B1 mutations impair cytotoxic granule exocytosis and platelet dense granule function, directly linking AP-3-dependent sorting to immune cytotoxicity and hemostasis.

    Evidence Flow cytometry for CD63 surface expression on CTL clones, CTL cytotoxicity assay, platelet aggregation and serotonin uptake in HPS2 patients

    PMID:19679886

    Open questions at the time
    • Whether lytic granule cargo is missorted or simply reduced not distinguished
    • Number of patients studied limited
  7. 2024 Medium

    iPSC-derived neutrophil modeling revealed that AP3B1 deficiency causes increased surface CD63, impaired degranulation, and reduced neutrophil output due to macrophage-mediated phagocytosis of maturing neutrophils, providing a cellular mechanism for the neutropenia seen in HPS2.

    Evidence HPS2 patient iPSC differentiation, flow cytometry, NADPH oxidase assay, microscopic analysis of macrophage phagocytosis

    PMID:38238087

    Open questions at the time
    • Signals triggering macrophage phagocytosis of AP3B1-deficient neutrophils not identified
    • Whether this mechanism operates in vivo in patient bone marrow not confirmed
  8. 2024 Medium

    AP3B1 was shown to function in antiviral defense: it restricts SARS-CoV-2 replication through interaction with the viral E protein and is required for PDIA3-triggered selective autophagy of rabies virus G protein, expanding AP-3 function beyond constitutive cargo sorting to pathogen restriction.

    Evidence Co-immunoprecipitation with SARS-CoV-2 E protein, overexpression/knockdown viral replication assays; AP-MS identifying PDIA3 interaction, AP3B1 KO abrogating G protein degradation

    PMID:39128851 PMID:39339853

    Open questions at the time
    • Whether antiviral function is AP-3 complex-dependent or β3A-specific not determined
    • Mechanism by which AP3B1 enables selective autophagy cargo recognition not elucidated
    • Both findings from single labs awaiting independent replication

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis of AP3B1 interactions with cargo sorting signals, the in vivo relevance of IP7-mediated pyrophosphorylation for endogenous trafficking, and the molecular mechanism by which AP3B1 participates in selective autophagy.
  • No high-resolution structure of AP-3 complex available
  • In vivo pyrophosphorylation site mapping and functional consequence not established
  • Selective autophagy mechanism through AP3B1-PDIA3 axis not reconstituted

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 4
Localization
GO:0005768 endosome 3 GO:0031410 cytoplasmic vesicle 3 GO:0005794 Golgi apparatus 2
Pathway
R-HSA-5653656 Vesicle-mediated transport 5 R-HSA-9609507 Protein localization 4 R-HSA-168256 Immune System 3 R-HSA-9612973 Autophagy 1
Partners
HPS1KIF3APDIA3
Complex memberships
AP-3 adaptor complex

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 AP3B1 encodes the β3A subunit of the AP-3 adaptor complex, which regulates protein trafficking in the trans-Golgi network/endosomal compartments; mutations in Ap3b1 (large internal tandem duplication and deletion) abrogate β3A function and cause defects in lysosomes, melanosomes, and platelet dense granules in pearl mice. Positional/candidate cloning, identification of mutations in pearl alleles, northern blot showing lowered expression Human molecular genetics High 9931340
2000 Loss of Ap3b1 function causes mislocalization of lysosomal membrane proteins LAMP-I and LAMP-II (clustered on cell surface) and melanosomal membrane protein tyrosinase in fibroblasts and melanocytes, demonstrating that AP-3 mediates an intracellular pathway for cargo transport to lysosomes/melanosomes that bypasses the plasma membrane route. Homologous recombination knockout of Ap3b1 in mice, immunofluorescence analysis of cultured fibroblasts and melanocytes Journal of cell science High 11058094
2002 Complete β3A deficiency due to nonsense mutations in ADTB3A (AP3B1) causes absence of the associated μ3 subunit of AP-3, and in fibroblasts results in aberrant trafficking of LAMP-3 (CD63) to the plasma membrane instead of the lysosome, confirming AP-3 complex integrity requires β3A and that the complex directs lysosomal membrane protein sorting. Patient genomic sequencing, immunoblotting showing absence of β3A and μ3 subunits, cell biological trafficking assay of LAMP-3 in fibroblasts Pediatric research High 11809908
2002 HPS1 (pale ear) and AP3B1/HPS2 (pearl) gene products function largely independently to affect production and function of melanosomes, lysosomes, and platelet dense granules; double mutant mice show additive/synergistic defects in all three organelle types, establishing these two genes act in parallel pathways. Genetic epistasis via double mutant mouse breeding, analysis of coat color, retinal pigment epithelium melanosomes, lysosomal enzyme secretion, and platelet serotonin levels Blood High 11861280
2006 A homozygous genomic deletion in AP3B1 causing in-frame skipping of exon 15 perturbs proper assembly of the heterotetrameric AP-3 complex and results in aberrant trafficking of CD63 (a transmembrane lysosomal protein), with additional consequences including degradation of melanosomes in keratinocytes and reduction of NK and NKT cell numbers. Genetic linkage analysis, targeted gene sequencing, cell biological trafficking assay of CD63, electron microscopy of keratinocytes, immunological assessment Blood High 16537806
2009 AP3B1 (β3A subunit of AP-3) is a substrate for IP7 (inositol pyrophosphate)-mediated pyrophosphorylation on a prephosphorylated serine residue; this pyrophosphorylation modulates AP3B1's interaction with Kif3A (a kinesin-superfamily motor protein), and both AP-3 and Kif3A are required for an intracellular process supporting HIV-1 Gag release. In vitro pyrophosphorylation assay, co-immunoprecipitation identifying Kif3A as AP3B1 binding partner, HIV-1 virus-like particle release assay with loss-of-function Proceedings of the National Academy of Sciences of the United States of America High 19934039
2009 AP3B1 mutations (frameshift deletions) in HPS2 patients cause increased surface expression of CD63 on cytotoxic T lymphocytes (CTLs) and impaired CTL cytotoxicity, as well as impaired platelet aggregation and reduced serotonin uptake, consistent with CTL granule and platelet dense granule defects due to AP-3 dysfunction. Patient mutation analysis, flow cytometry for CD63 surface expression on CTL clones, CTL cytotoxicity assay, platelet aggregation and 3H-serotonin uptake assay Haematologica Medium 19679886
2014 Ap3b1 (pearl) gene plays a distinct role from Hps1 in ocular melanosome biogenesis: pearl mice show more severe hypopigmentation in neural crest-derived ocular tissues but stronger total tyrosinase activity (less degradation of aberrantly transported tyrosinase) compared to pale ear (Hps1) mice; double heterozygotes show additive iris hypopigmentation, indicating non-redundant pathway functions. Comparative mouse genetics, tyrosinase activity assays in eyes, histological pigmentation analysis, double heterozygote breeding Experimental eye research Medium 25160823
2024 AP3B1 interacts with the SARS-CoV-2 envelope (E) protein in virus-infected cells; overexpression of AP3B1 suppresses SARS-CoV-2 replication while siRNA-mediated depletion increases release of infectious virus, demonstrating an antiviral function for AP3B1 through its interaction with the viral E protein. Co-immunoprecipitation of AP3B1 with SARS-CoV-2 E protein in infected cells, immunofluorescence, AP3B1 overexpression and siRNA knockdown with viral replication/release assays Viruses Medium 39339853
2024 AP3B1 is indispensable for PDIA3-triggered selective autophagy-mediated degradation of rabies virus G protein; AP3B1 interacts with PDIA3 (identified by affinity tag-purification mass spectrometry), and AP3B1 knockout abrogates PDIA3-mediated G protein degradation, implicating AP3B1 in selective macroautophagy of viral cargo. Affinity tag-purification mass spectrometry, co-immunoprecipitation, AP3B1 knockout cell lines, autophagy/degradation assays Autophagy Medium 39128851
2004 The causative mutation in canine cyclic neutropenia is an insertion of an extra adenine in a poly-A tract in exon 21 of the AP3B1 gene; transcription through homopolymeric adenine sequences is error-prone, producing a mixture of in-frame and out-of-frame transcripts, with preferential accumulation of normal-length mRNA from mutant alleles due to nonsense-mediated degradation of out-of-frame transcripts. RT-PCR subclone analysis of transcripts from homozygous and heterozygous dogs, in vitro reporter assay for transcriptional fidelity Nucleic acids research Medium 15576359
2024 In HPS2 iPSC-derived neutrophil cultures, AP3B1-deficient neutrophils show increased surface CD63 expression and impaired degranulation capacity; additionally, HPS2 neutrophil output is reduced due to macrophage-mediated phagocytosis of maturing neutrophils, revealing a role for AP3B1 in neutrophil granule protein sorting and neutrophil survival during maturation. iPSC differentiation model, flow cytometry for CD63 and degranulation markers, NADPH oxidase activity assay, microscopic analysis of macrophage phagocytosis Life science alliance Medium 38238087

Source papers

Stage 0 corpus · 27 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 213 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
2002 The Hermansky-Pudlak syndrome 1 (HPS1) and HPS2 genes independently contribute to the production and function of platelet dense granules, melanosomes, and lysosomes. Blood 51 11861280
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 29 33867526
2013 Disruption of AP3B1 by a chromosome 5 inversion: a new disease mechanism in Hermansky-Pudlak syndrome type 2. BMC medical genetics 25 23557002
2000 Genomic structure of the mouse Ap3b1 gene in normal and pearl mice. Genomics 22 11056055
1999 Delayed expression of hpS2 and prolonged expression of CIP1/WAF1/SDI1 in human tumour cells irradiated with X-rays, fission neutrons or 1 GeV/nucleon Fe ions. International journal of radiation biology 19 10374935
2015 Synergistic defects of UNC13D and AP3B1 leading to adult hemophagocytic lymphohistiocytosis. International journal of hematology 16 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 9 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 Reduced myeloid commitment and increased uptake by macrophages of stem cell-derived HPS2 neutrophils. Life science alliance 1 38238087
2024 AP3B1 Has Type I Interferon-Independent Antiviral Function against SARS-CoV-2. Viruses 1 39339853
2016 Generation of Hermansky Pudlak syndrome type 2 (HPS2) induced pluripotent stem cells (iPSCs). Stem cell research 1 27345985
2025 Synergistic blood-based diagnostic value of AP3B1 and BMPR2 in Parkinson's disease. NPJ Parkinson's disease 0 41152257
2025 Canine Neuronal Ceroid Lipofuscinosis-like Disorder Associated with Sequence Variants in AP3B1 and TRAPPC9. Genes 0 41300827
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