AP3B1

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0016192 vesicle-mediated transport	IBA GO_REF:0000033	ACCEPT	Summary: AP3B1, as the beta subunit of the AP-3 adaptor complex, is directly involved in vesicle-mediated transport. AP-3 mediates the sorting and trafficking of cargo proteins from the TGN and endosomes to lysosomes and LROs via coated vesicles (PMID:9151686, PMID:9545220). Reason: This is a well-established core function of AP-3. The complex mediates vesicle formation and cargo selection for transport to lysosomes and LROs. IBA annotation is phylogenetically supported. Supporting Evidence: PMID:9151686 Immunofluorescence using anti-delta antibodies reveals that the AP-3 complex is associated with the Golgi region of the cell as well as with more peripheral structures. PMID:9545220 AP-3 has been proposed to be a component of a nonclathrin coat. In vitro binding assays showed that mammalian AP-3 did associate with clathrin by interaction of the appendage domain of its beta3 subunit with the amino-terminal domain of the clathrin heavy chain.
GO:0048490 anterograde synaptic vesicle transport	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: This annotation refers to neuron-specific transport functions. While AP-3 has neuronal-specific isoforms (AP3B2), the ubiquitous AP3B1 isoform also contributes to synaptic vesicle protein sorting in neurons according to phylogenetic inference. Reason: AP3B1 is the ubiquitous isoform, while AP3B2 is the neuron-specific beta subunit. However, ubiquitous AP-3 still contributes to synaptic vesicle biogenesis in neurons. This is a legitimate but non-core function for the ubiquitous isoform. The IBA annotation is from phylogenetic inference and includes mouse AP3B1 orthologs. Supporting Evidence: file:human/AP3B1/AP3B1-deep-research-cyberian.md The brain expresses both ubiquitous (AP-3A, containing beta3A encoded by AP3B1) and neuronal-specific (AP-3B, containing beta3B encoded by AP3B2) forms of the AP-3 complex. Studies in mice and in vitro reconstitution experiments have demonstrated that only the neuronal form of AP-3 can generate synaptic vesicles from endosomes, despite being the minority form quantitatively in brain tissue. PMID:11588176 However, only the neuronal form of AP-3 can produce synaptic vesicles from endosomes in vitro
GO:0005794 Golgi apparatus	IEA GO_REF:0000044	ACCEPT	Summary: AP-3 localizes to the trans-Golgi network as demonstrated by immunofluorescence and immunoelectron microscopy (PMID:9151686). This IEA annotation from UniProt subcellular location mapping is accurate. Reason: Direct experimental evidence from the original characterization of AP-3 demonstrates Golgi localization. Simpson et al. (1997) showed AP-3 association with the Golgi region. Supporting Evidence: PMID:9151686 Immunofluorescence using anti-delta antibodies reveals that the AP-3 complex is associated with the Golgi region of the cell as well as with more peripheral structures.
GO:0006886 intracellular protein transport	IEA GO_REF:0000002	ACCEPT	Summary: AP-3 is involved in intracellular protein transport, specifically sorting transmembrane proteins to lysosomes and LROs. This annotation from InterPro domain mapping accurately reflects the adaptin function. Reason: This is consistent with the established role of AP-3 in sorting proteins. The InterPro domains (IPR002553, IPR015151) correctly associate with this transport function. Supporting Evidence: PMID:9931340 The beta3A subunit of the AP-3 adaptor complex, which likely regulates protein trafficking in the trans - Golgi network/endosomal compartments
GO:0015031 protein transport	IEA GO_REF:0000043	ACCEPT	Summary: General protein transport annotation based on UniProt keyword mapping. While accurate, this is very broad - the more specific GO:0006886 (intracellular protein transport) is more informative. Reason: This IEA annotation is accurate but general. It is acceptable to keep as it correctly captures that AP3B1 is involved in protein transport, even if less specific than other annotations.
GO:0016192 vesicle-mediated transport	IEA GO_REF:0000002	ACCEPT	Summary: Duplicate of the IBA annotation for vesicle-mediated transport, this one inferred from InterPro domains. Both annotations are valid. Reason: This annotation via InterPro mapping correctly captures the vesicle transport function of AP-3 adaptor complexes. Having both IBA and IEA evidence is acceptable.
GO:0030117 membrane coat	IEA GO_REF:0000002	ACCEPT	Summary: AP-3 functions as a membrane coat complex, forming the protein scaffold on the cytoplasmic side of coated vesicles. This annotation correctly reflects the structural role of AP-3. Reason: AP-3 is indeed a component of the membrane coat, functioning like other adaptor complexes to form vesicle coats. Supporting Evidence: PMID:9151686 the complex is required for a nonclathrin-mediated budding event from the TGN
GO:0030123 AP-3 adaptor complex	IEA GO_REF:0000002	ACCEPT	Summary: AP3B1 is definitively a component of the AP-3 adaptor complex, providing the beta subunit of the heterotetrameric complex (beta, delta, mu, sigma subunits). Reason: This is the defining cellular component annotation for AP3B1. Multiple studies confirm AP3B1 as the beta-3A subunit of AP-3. Supporting Evidence: PMID:9151686 We are calling this complex AP-3, by analogy with AP-1 and AP-2
GO:0030131 clathrin adaptor complex	IEA GO_REF:0000002	ACCEPT	Summary: AP-3 associates with clathrin via the beta3 subunit appendage domain, making this annotation accurate. However, AP-3 can also function in clathrin-independent pathways. Reason: While there is evidence for clathrin-independent AP-3 function in some contexts, the complex does bind clathrin via the beta3 subunit. This annotation is broadly correct. Supporting Evidence: PMID:9545220 In vitro binding assays showed that mammalian AP-3 did associate with clathrin by interaction of the appendage domain of its beta3 subunit with the amino-terminal domain of the clathrin heavy chain.
GO:0030665 clathrin-coated vesicle membrane	IEA GO_REF:0000044	ACCEPT	Summary: UniProt subcellular location annotation. AP-3 localizes to clathrin-coated vesicle membranes as part of its adaptor function. Reason: This annotation from UniProt subcellular location is consistent with the experimental evidence for AP-3 colocalization with clathrin. Supporting Evidence: PMID:9545220 AP-3 colocalized with clathrin in cells as observed by immunofluorescence and immunoelectron microscopy.
GO:0031410 cytoplasmic vesicle	IEA GO_REF:0000043	ACCEPT	Summary: General localization to cytoplasmic vesicles. This is accurate but less specific than other cellular component annotations. Reason: AP-3 does localize to cytoplasmic vesicles. This broad annotation is acceptable as a general localization term.
GO:1904115 axon cytoplasm	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: This annotation is inferred from GO:0008089 (anterograde axonal transport) and GO:0048490 (anterograde synaptic vesicle transport). It represents neuronal localization. Reason: While AP3B1 may localize to axon cytoplasm in neurons, this is not a core localization for the ubiquitous isoform. The annotation is computationally inferred from process annotations that are themselves non-core for AP3B1.
GO:0005515 protein binding	IPI PMID:24725412 Ribosomal protein s15 phosphorylation mediates LRRK2 neurode...	MARK AS OVER ANNOTATED	Summary: This IPI annotation indicates AP3B1 binds to LRRK2 (Q5S007). This interaction is relevant to Parkinson's disease research but represents a generic protein binding annotation. Reason: Generic "protein binding" annotations are not informative. The underlying interaction with LRRK2 is legitimate from high-throughput studies, but a more specific MF term would be preferable if the functional nature of the interaction were known. Supporting Evidence: PMID:24725412 Ribosomal protein s15 phosphorylation mediates LRRK2 neurodegeneration in Parkinson's disease.
GO:0005515 protein binding	IPI PMID:27424887 LRRK2 and RAB7L1 coordinately regulate axonal morphology and...	MARK AS OVER ANNOTATED	Summary: Another IPI annotation for AP3B1 binding to LRRK2 from a different study on axonal morphology and lysosome integrity. Reason: Same as above - generic protein binding is not informative. The interaction is real but the annotation does not capture specific function. Supporting Evidence: PMID:27424887 LRRK2 and RAB7L1 coordinately regulate axonal morphology and lysosome integrity in diverse cellular contexts.
GO:0005515 protein binding	IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ...	MARK AS OVER ANNOTATED	Summary: IPI annotation from interactome mapping study with multiple neurodegenerative disease proteins (ALS2, DNALI1, HTT, SNCA, OPTN, BAG6). Reason: High-throughput interactome mapping generates many protein binding annotations. While the interactions may be real, generic protein binding is uninformative. These are likely incidental interactions rather than functional molecular activities. Supporting Evidence: PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains.
GO:0008089 anterograde axonal transport	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Inferred from mouse ortholog (Q9Z1T1) via Ensembl Compara. This neuronal process annotation is transferred from experimental data in mouse. Reason: While AP3B1 contributes to neuronal vesicle transport, this is not the core function of the ubiquitous isoform. The neuron-specific AP3B2 is the primary beta subunit for neuronal AP-3 functions.
GO:0048490 anterograde synaptic vesicle transport	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Duplicate of the IBA annotation, this one inferred from mouse ortholog via Ensembl. Reason: Same reasoning as the IBA annotation - this is a neuronal function that is non-core for the ubiquitous AP3B1 isoform.
GO:1990742 microvesicle	IEA GO_REF:0000107	UNDECIDED	Summary: Localization to microvesicles inferred from mouse ortholog. Microvesicles are extracellular vesicles shed from the plasma membrane. Reason: The evidence for AP3B1 localization to microvesicles is not clearly established in the literature I have reviewed. This may be an artifact of high-throughput proteomic studies. More evidence is needed.
GO:0005769 early endosome	NAS PMID:23247405 Cell type-specific Rab32 and Rab38 cooperate with the ubiqui...	ACCEPT	Summary: AP-3 localizes to early/recycling endosomal domains where it functions in cargo sorting for transport to melanosomes and lysosomes (PMID:23247405). Reason: This is a well-supported localization. AP-3 functions at early endosomal tubular domains to sort cargo for delivery to LROs and lysosomes. Supporting Evidence: PMID:23247405 The localization of Rab32 and Rab38 is likely to specific tubular domains of early/recycling endosomes that contain AP-1, AP-3 or BLOC-2.
GO:0016192 vesicle-mediated transport	NAS PMID:23247405 Cell type-specific Rab32 and Rab38 cooperate with the ubiqui...	ACCEPT	Summary: Third annotation for vesicle-mediated transport, this one NAS from the Bultema/Di Pietro review on LRO biogenesis. Reason: Consistent with the IBA and IEA annotations. Multiple evidence sources support this core function. Supporting Evidence: PMID:23247405 Cell type-specific Rab32 and Rab38 cooperate with the ubiquitous lysosome biogenesis machinery to synthesize specialized lysosome-related organelles.
GO:0035654 clathrin-coated vesicle cargo loading, AP-3-mediated	NAS PMID:9545220 Association of the AP-3 adaptor complex with clathrin.	ACCEPT	Summary: This highly specific term captures the precise molecular function of AP-3 in cargo loading into clathrin-coated vesicles. This is derived from the original Dell'Angelica et al. 1998 paper on AP-3-clathrin association. Reason: This is an excellent, specific annotation that accurately describes the AP-3 function. The original paper demonstrated AP-3 association with clathrin and cargo loading function. Supporting Evidence: PMID:9545220 A heterotetrameric complex termed AP-3 is involved in signal-mediated protein sorting to endosomal-lysosomal organelles.
GO:0060155 platelet dense granule organization	NAS PMID:23247405 Cell type-specific Rab32 and Rab38 cooperate with the ubiqui...	ACCEPT	Summary: AP-3 is required for the biogenesis of platelet dense granules, which are LROs. Loss of AP3B1 in HPS-2 results in platelet storage pool deficiency. Reason: This is a well-established core function. HPS-2 patients have bleeding disorders due to absent/reduced platelet dense granules. Supporting Evidence: PMID:23247405 Hermansky-Pudlak Syndrome (HPS) patients and the corresponding animal models have abnormal melanosomes, platelet dense granules and lamellar bodies of lung type II epithelial cells. file:human/AP3B1/AP3B1-deep-research-falcon.md platelet dense-granule deficiency causing bleeding diathesis
GO:1903232 melanosome assembly	NAS PMID:23247405 Cell type-specific Rab32 and Rab38 cooperate with the ubiqui...	ACCEPT	Summary: AP-3 is essential for melanosome biogenesis, trafficking melanogenic enzymes like tyrosinase to maturing melanosomes. Reason: This is a core function of AP-3. Loss of AP3B1 causes hypopigmentation due to defective melanosome biogenesis in HPS-2. Supporting Evidence: PMID:11452004 AP-3 mediates tyrosinase but not TRP-1 trafficking in human melanocytes. PMID:23247405 Mutations in subunits of AP-3, BLOC-1, BLOC-2 and BLOC-3 underlie many forms of HPS.
GO:0030742 GTP-dependent protein binding	IPI PMID:22511774 BLOC-2, AP-3, and AP-1 proteins function in concert with Rab...	ACCEPT	Summary: AP-3 binds to Rab32 and Rab38 in a GTP-dependent manner, with preferential binding to the GTP-bound active form of these Rab GTPases (PMID:22511774). Reason: This is a meaningful molecular function annotation. The GTP-dependent binding to Rab32/38 is essential for AP-3 function in LRO biogenesis and is more informative than generic protein binding. Supporting Evidence: PMID:22511774 BLOC-2, AP-3, and AP-1 coimmunoprecipitated with Rab38 and Rab32 from MNT-1 melanocytic cell extracts. PMID:23247405 In GST-Rab pulldown assays, Rab32 and Rab38 showed preferential binding to BLOC-2, AP-1 and AP-3 when bound to GTP instead of GDP.
GO:0016020 membrane	HDA PMID:19946888 Defining the membrane proteome of NK cells.	ACCEPT	Summary: General membrane localization from proteomics study defining NK cell membrane proteome. Reason: AP-3 does associate with membranes (TGN, endosomal, vesicular membranes). This is a very general annotation but accurate. Supporting Evidence: PMID:19946888 Defining the membrane proteome of NK cells.
GO:0005765 lysosomal membrane	HDA PMID:17897319 Integral and associated lysosomal membrane proteins.	ACCEPT	Summary: Lysosomal membrane localization from high-throughput proteomics study on lysosomal membrane proteins. Reason: AP-3 functions in trafficking to lysosomes, and the complex may transiently associate with lysosomal membranes during cargo delivery. This is consistent with its function in lysosomal biogenesis. Supporting Evidence: PMID:17897319 2007 Sep 26. Integral and associated lysosomal membrane proteins.
GO:0008089 anterograde axonal transport	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: Manually transferred from mouse ortholog (Q9Z1T1) based on sequence similarity. Reason: Same reasoning as IEA version - neuronal function that is non-core for the ubiquitous AP3B1 isoform.
GO:0048490 anterograde synaptic vesicle transport	ISS GO_REF:0000024	KEEP AS NON CORE	Summary: Manually transferred from mouse ortholog based on sequence similarity. Reason: Same reasoning - non-core neuronal function for ubiquitous isoform.
GO:0032438 melanosome organization	IMP PMID:11452004 AP-3 mediates tyrosinase but not TRP-1 trafficking in human ...	ACCEPT	Summary: Direct experimental evidence (IMP) from Huizing et al. 2001 showing AP-3 is required for proper melanosome organization. HPS-2 melanocytes show abnormal tyrosinase trafficking and melanosome defects. Reason: This is strong experimental evidence from mutant phenotype analysis. Loss of AP3B1 in HPS-2 cells causes melanosome organization defects. Supporting Evidence: PMID:11452004 tyrosinase exhibited a melanosomal (i.e., perinuclear and dendritic) pattern in normal cells but only a perinuclear pattern in the HPS-2 melanocytes. In addition, tyrosinase exhibited a normal pattern of expression in HPS-2 melanocytes transfected with a cDNA encoding the beta 3A subunit of the AP-3 complex.
GO:0032438 melanosome organization	IMP PMID:19841138 AP-1 and KIF13A coordinate endosomal sorting and positioning...	ACCEPT	Summary: Additional IMP evidence for melanosome organization from Delevoye et al. 2009 study on AP-1 and KIF13A in melanosome biogenesis, which also discusses AP-3 function. Reason: Additional experimental support for the melanosome organization function. This study provides context for AP-3 function in endosomal sorting for melanosomes. Supporting Evidence: PMID:19841138 Studies in melanocytes from HPS patients and their mouse models revealed that cargoes destined for melanosomes emerge from distinct domains on early endosomes by at least two pathways that require AP-3 and BLOC-1/BLOC-2, respectively
GO:0019903 protein phosphatase binding	IPI PMID:17622474 Involvement of beta3A subunit of adaptor protein-3 in intrac...	ACCEPT	Summary: AP3B1 binds to the receptor tyrosine phosphatase PCP-2/PTPRU (Q92729) as shown by yeast two-hybrid and confirmed in mammalian cells (PMID:17622474). Reason: This is a specific, experimentally validated interaction. The binding to PCP-2 suggests a role for AP-3 in trafficking this phosphatase, which is more informative than generic protein binding. Supporting Evidence: PMID:17622474 The association between the beta3A subunit of AP-3 and PCP-2 was further confirmed in mammalian cells. Our results suggested a possible mechanism of intracellular trafficking of PCP-2 mediated by AP-3
GO:0005794 Golgi apparatus	TAS PMID:9151686 Characterization of the adaptor-related protein complex, AP-...	ACCEPT	Summary: Traceable Author Statement from the original Simpson et al. 1997 paper characterizing AP-3, showing Golgi localization. Reason: Direct reference to experimental evidence from the original AP-3 characterization paper. Supporting Evidence: PMID:9151686 Immunofluorescence using anti-delta antibodies reveals that the AP-3 complex is associated with the Golgi region of the cell
GO:0006886 intracellular protein transport	TAS PMID:9931340 The beta3A subunit gene (Ap3b1) of the AP-3 adaptor complex ...	ACCEPT	Summary: TAS annotation from the pearl mouse study (Feng et al. 1999) which established that AP3B1 mutations cause defects in protein trafficking to lysosomes and LROs. Reason: This paper provides key evidence linking AP3B1 to intracellular protein transport through the pearl mouse model. Supporting Evidence: PMID:9931340 The beta3A subunit of the AP-3 adaptor complex, which likely regulates protein trafficking in the trans - Golgi network/endosomal compartments

Gene Description

Existing Annotations Review

Core Functions

AP3B1 is the beta-3A subunit of the heterotetrameric AP-3 adaptor complex. This is the defining structural role - without AP3B1, the AP-3 complex cannot assemble or function properly.

AP-3 recognizes cargo proteins with dileucine or tyrosine-based sorting signals and loads them into coated vesicles for transport to lysosomes and LROs. This cargo selection function is essential for proper protein sorting to melanosomes and platelet dense granules.

References

Deep Research

Cyberian

Falcon

Perplexity

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