Affinage

AAGAB

Alpha- and gamma-adaptin-binding protein p34 · UniProt Q6PD74

Length
315 aa
Mass
34.6 kDa
Annotated
2026-06-09
17 papers in source corpus 10 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

AAGAB (p34) is an assembly chaperone for heterotetrameric clathrin adaptor protein complexes, nucleating the formation of AP1, AP2, and AP4 that drive clathrin-mediated membrane trafficking (PMID:31353312, PMID:34494650, PMID:35976721). It uses two functionally distinct modules: an N-terminal type I pseudoGTPase domain (catalytically inactive) that engages and stabilizes the small σ subunits of AP1 and AP2 through an interface distinct from conventional GTPase contacts, and a C-terminal dimerization domain that recognizes the γ subunit of AP1 and the α subunit of AP2 using a shared surface; AAGAB exists as a homodimer that transitions to monomer upon binding adaptor subunits (PMID:36598941). By guiding the sequential, ordered association of adaptor subunits and stabilizing partially assembled intermediates, AAGAB prevents the degradation that otherwise destroys unassembled subunits (PMID:31353312, PMID:34494650). For AP2, AAGAB initiates assembly by forming an AAGAB:α:σ2 complex that is then handed off to CCDC32, which completes tetramer assembly before release (PMID:39145939). Loss of AAGAB collapses adaptor assembly, broadly remodeling surface protein homeostasis, impairing endocytic recycling of growth factor receptors such as EGFR, and causing accumulation of the AP4 cargo ATG9A at the trans-Golgi network (PMID:23064416, PMID:34494650, PMID:35976721). Nonsense and CTD-truncating mutations in AAGAB destabilize the protein and abolish chaperone function, causing punctate palmoplantar keratoderma (PPKP1) (PMID:23000146, PMID:36598941). AAGAB additionally supports clathrin-mediated synaptic vesicle recycling and neurotransmitter release in neurons (PMID:38253235), and in hypoxic-ischemic injury models acts upstream of the E3 ligase NEDD4-1 to control ubiquitination of PTEN and SHIP2 (PMID:33712741, PMID:41412220).

Mechanistic history

Synthesis pass · year-by-year structured walk · 10 steps
  1. 2012 Medium

    Established the first link between AAGAB and membrane trafficking by showing it binds clathrin adaptor complexes and that its loss perturbs growth factor receptor handling.

    Evidence Adaptin binding assays and siRNA knockdown in keratinocytes with EGFR readouts

    PMID:23064416

    Open questions at the time
    • Did not define which adaptor subunits AAGAB contacts
    • Did not establish whether AAGAB acts in assembly versus another step
    • EGFR effect inferred indirectly from expression and phosphorylation
  2. 2012 Medium

    Connected AAGAB loss-of-function mutations to disease, showing nonsense alleles undergo nonsense-mediated decay and that protein loss alters AAGAB subcellular distribution in patient cells.

    Evidence Immunoblot, mRNA analysis, and immunofluorescence in patient keratinocytes

    PMID:23000146

    Open questions at the time
    • Molecular mechanism connecting AAGAB loss to keratoderma not defined
    • Perinuclear redistribution not mechanistically explained
  3. 2019 High

    Defined AAGAB's core mechanism as an assembly chaperone that orders AP2 subunit association and stabilizes intermediates, explaining why subunits are degraded in its absence.

    Evidence Genome-wide CME screen plus biochemical reconstitution of AP2 assembly and subunit stability assays, with disease mutation tested

    PMID:31353312

    Open questions at the time
    • Did not resolve which AAGAB domains bind which subunits
    • Did not address AP1 or AP4
    • Final assembly steps beyond AAGAB-bound intermediate unresolved
  4. 2021 High

    Generalized the chaperone role beyond AP2 by showing AAGAB stabilizes AP1 γ and σ subunits and that combined AP1/AP2 deficiency drives broad surface proteome remodeling, while excluding AP3.

    Evidence Co-IP, AP1 assembly assays, surface proteomics, and cargo trafficking in AAGAB mutant cells

    PMID:34494650

    Open questions at the time
    • Did not test AP4
    • Structural basis of subunit recognition not resolved
  5. 2022 High

    Extended AAGAB chaperone activity to AP4, linking it to the autophagy-related cargo ATG9A.

    Evidence Co-IP, AAGAB knockout cells, AP4 subunit immunoblots, and ATG9A localization imaging

    PMID:35976721

    Open questions at the time
    • Did not determine whether AP4 assembly uses the same domains/handover as AP2
    • Functional consequences of ATG9A mislocalization for autophagy not assessed
  6. 2023 High

    Resolved the structural logic of the C-terminal domain, showing AAGAB is a homodimer that monomerizes on binding and uses one shared CTD surface for both AP1 γ and AP2 α, and that disease truncations destabilize this module.

    Evidence X-ray crystallography of the CTD, dimerization and AP subunit binding assays, patient mutant analysis

    PMID:36598941

    Open questions at the time
    • Did not resolve the N-terminal σ-binding interface
    • Did not capture a full AAGAB:adaptor co-structure
  7. 2024 High

    Defined the AP2 maturation pathway downstream of AAGAB as a chaperone handover, where AAGAB:α:σ2 is transferred to CCDC32 for completion of tetramer assembly.

    Evidence Biochemical reconstitution of sequential assembly, co-IP, and mutant analysis

    PMID:39145939

    Open questions at the time
    • Did not establish whether AP1/AP4 use analogous handover factors
    • Trigger for AAGAB release and CCDC32 capture not fully defined
  8. 2024 High

    Identified the N-terminal region as a catalytically dead type I pseudoGTPase and showed structurally how it stabilizes adaptor σ subunits via a non-canonical interface.

    Evidence X-ray crystallography of the psGD:AP1σ3 complex, binding assays, interface mutagenesis, and cell-based trafficking assays (preprint)

    Open questions at the time
    • Preprint, not yet peer-reviewed
    • Did not integrate psGD and CTD into a single full-length assembly model
  9. 2024 Medium

    Demonstrated a neuronal requirement for AAGAB in clathrin-mediated synaptic vesicle recycling and neurotransmitter release, with mRNA rescue confirming specificity.

    Evidence Zebrafish aagab loss-of-function, calcium imaging, local field potentials, FM 1-43 release in knockdown cells, and mRNA rescue

    PMID:38253235

    Open questions at the time
    • Did not establish whether the neuronal phenotype is mediated specifically through AP2 versus other adaptors
    • Single model system
  10. 2025 Medium

    Placed AAGAB in a NEDD4-1-centered ubiquitination axis controlling PTEN and SHIP2 in hypoxic-ischemic injury, distinct from its adaptor chaperone role.

    Evidence In vivo rat HIBD/HIE models, OGD neuronal models, lentiviral overexpression/knockdown, co-IP, ubiquitination, and ROS/mitochondrial assays

    PMID:33712741 PMID:41412220

    Open questions at the time
    • Mechanism by which AAGAB controls NEDD4-1 protein level not defined
    • Relationship between adaptor chaperone function and NEDD4-1 regulation unresolved
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • How AAGAB's two roles — adaptor assembly chaperone and NEDD4-1 regulator — are mechanistically related, and whether a single full-length structural model integrating the pseudoGTPase and CTD modules across AP1/AP2/AP4 assembly exists, remains unresolved.
  • No full-length AAGAB:adaptor structure
  • Mechanism linking AAGAB to NEDD4-1 protein stability unknown
  • Whether AP1/AP4 require dedicated handover factors like CCDC32 is untested

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0044183 protein folding chaperone 4 GO:0140096 catalytic activity, acting on a protein 3 GO:0098772 molecular function regulator activity 2
Localization
GO:0005794 Golgi apparatus 2 GO:0005829 cytosol 1
Pathway
R-HSA-5653656 Vesicle-mediated transport 3 R-HSA-392499 Metabolism of proteins 2 R-HSA-9609507 Protein localization 2
Partners
AP1G1AP1S3AP2A1AP2S1AP4E1CCDC32NEDD4-1

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2012 AAGAB (p34) binds both α- and γ-adaptin clathrin adaptor protein complexes (AP1 and AP2), indicating a role in membrane trafficking. Knockdown of AAGAB in keratinocytes led to increased cell division linked to elevated EGFR protein expression and tyrosine phosphorylation, suggesting p34 deficiency impairs endocytic recycling of growth factor receptors. Protein-protein binding assays (adaptin binding), siRNA knockdown in keratinocytes with immunoblot/phosphorylation readout, ultrastructural analysis of vesicle biology Nature genetics Medium 23064416
2012 Nonsense mutations in AAGAB cause premature translation termination; the disease allele mRNA is absent or at low levels (nonsense-mediated decay). In affected individual keratinocytes, AAGAB immunofluorescence staining shifts from cytoplasmic granular distribution to perinuclear accumulation. Immunoblot, mRNA analysis, immunofluorescence in patient skin keratinocytes American journal of human genetics Medium 23000146
2019 AAGAB controls AP2 adaptor complex assembly in clathrin-mediated endocytosis. AAGAB guides the sequential association of AP2 subunits and stabilizes assembly intermediates; without AAGAB, AP2 subunits fail to form the complex and are degraded. A disease-causing PPKP1 mutation abrogates this function. Genome-wide genetic screen of CME, biochemical reconstitution of AP2 assembly, loss-of-function cell studies with AP2 subunit stability assays Developmental cell High 31353312
2021 AAGAB also regulates assembly of AP1 (involved in trans-Golgi network to endosome transport) by binding and stabilizing the γ and σ subunits of AP1. AAGAB mutation abolishes AP1 assembly and disrupts AP1-mediated cargo trafficking. AAGAB is not involved in AP3 complex formation. Loss of AAGAB massively alters surface protein homeostasis reflecting synergistic AP1 and AP2 deficiency. Co-immunoprecipitation, AP1 assembly assays, comparative proteomics of surface proteins, cargo trafficking assays, AAGAB mutant cell lines Journal of cell science High 34494650
2021 AAGAB acts as a novel regulator of NEDD4-1, controlling the level of NEDD4-1 protein, which in turn mediates mono-ubiquitination of PTEN at lysine 13 (K13) and promotes PTEN nuclear translocation during hypoxic-ischemic conditions. Genetic upregulation of Aagab reduced PTEN nuclear translocation and alleviated neurological deficits in HIBD model rats. In vivo rat HIBD model, OGD neuronal model, lentiviral overexpression, co-immunoprecipitation, ubiquitination assays, behavioral assays Cell death and differentiation Medium 33712741
2022 AAGAB binds to and stabilizes the AP-4 ε and σ4 subunits, promoting AP-4 complex assembly. AAGAB-knockout cells show reduced levels of AP-4 subunits and accumulation of ATG9A at the TGN, phenocopying AP-4 subunit mutations. Co-immunoprecipitation, AAGAB knockout cells, immunoblot for AP-4 subunit levels, immunofluorescence for ATG9A localization Molecular biology of the cell High 35976721
2023 AAGAB exists as a homodimer before AP1/2 binding, mediated by its C-terminal domain (CTD). The CTD undergoes an oligomer-to-monomer transition upon binding AP subunits, using the same CTD surface to recognize both the γ subunit of AP1 and the α subunit of AP2. Disease-causing PPKP1 mutations truncate the CTD, destabilizing AAGAB and abolishing chaperone function. Crystal structure of the dimerization CTD reveals an antiparallel dimer of bent helices. X-ray crystallography (CTD crystal structure), biochemical dimerization assays, binding assays with AP1 γ and AP2 α subunits, analysis of patient mutant proteins Proceedings of the National Academy of Sciences of the United States of America High 36598941
2024 AP2 assembly proceeds by an AAGAB-to-CCDC32 handover mechanism: AAGAB initiates AP2 assembly by stabilizing its α and σ2 subunits, forming an AAGAB:α:σ2 complex that cannot recruit further subunits. CCDC32 recognizes this complex and is handed off to form an α:σ2:CCDC32 ternary complex, which sequentially recruits µ2 and β2 subunits to complete AP2 assembly, with CCDC32 then released. A disease-causing mutation disrupts CCDC32's AP2-regulating function. Biochemical reconstitution, co-immunoprecipitation, mutant protein analysis, sequential assembly assays Proceedings of the National Academy of Sciences of the United States of America High 39145939
2024 The N-terminal region of AAGAB is a type i pseudoGTPase (catalytically inactive). The AAGAB pseudoGTPase domain (psGD) interacts with the σ subunits of AP1 and AP2 via a unique interface distinct from conventional GTPase-interacting regions. Crystal structure of the AAGAB psGD:AP1σ3 complex was solved, revealing the structural basis of σ subunit stabilization during adaptor complex assembly. X-ray crystallography (psGD:AP1σ3 crystal structure), biochemical binding assays, cell-based membrane trafficking assays, mutagenesis of the binding interface bioRxivpreprint High
2024 Loss of aagab in zebrafish causes impaired calcium responses and reduced local field potential in optic tectal neurons, reduced neurotransmitter (norepinephrine) release, and defective clathrin-mediated synaptic vesicle recycling (delayed FM 1-43 release in AAGAB-knockdown neuroblastoma cells). Overexpression of aagab mRNA restores neurotransmitter release, calcium responses, and swimming ability. Zebrafish aagab loss-of-function mutant, calcium imaging, local field potential recording, FM 1-43 dye release assay in knockdown neuroblastoma cells, mRNA rescue Journal of genetics and genomics Medium 38253235
2025 AAGAB overexpression increases NEDD4-1 protein levels, promotes SHIP2 ubiquitination, and accelerates SHIP2 degradation; NEDD4-1 knockdown reverses these effects, placing AAGAB upstream of NEDD4-1 in a regulatory axis that controls SHIP2 levels. This Aagab-NEDD4-1-SHIP2 axis alleviates mitochondrial oxidative stress in hypoxic-ischemic encephalopathy. Lentiviral overexpression and knockdown in OGD neuronal model and in vivo rat HIE model, ubiquitination assays, ROS measurement, mitochondrial membrane potential assay, behavioral assays Mitochondrion Medium 41412220
2025 CCDC32 interacts with the appendage domain of the AP-2 α subunit using canonical endocytic regulator binding sites plus a novel conserved pocket on α. CCDC32 amphipathic helices bind the α/σ2 heterodimer and also mediate binding to PIP2-containing membranes. In solution, CCDC32 prevents AP-2 complex assembly and actively disassembles AP-2 tetramers; the presence of PIP2-containing membrane acts as a molecular switch releasing inhibitory interactions to allow full assembly. Cryo-EM visualizes an assembly intermediate with CCDC32 bound at both cargo-binding and membrane-binding sites, mimicking vesicle-associated AP-2 conformation. In vitro reconstitution, cryo-EM structure, integrative structural analysis, PIP2-liposome binding assays, AP-2 disassembly assays bioRxivpreprint Medium

Source papers

Stage 0 corpus · 17 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 Haploinsufficiency for AAGAB causes clinically heterogeneous forms of punctate palmoplantar keratoderma. Nature genetics 70 23064416
2012 Nonsense mutations in AAGAB cause punctate palmoplantar keratoderma type Buschke-Fischer-Brauer. American journal of human genetics 54 23000146
2019 AAGAB Controls AP2 Adaptor Assembly in Clathrin-Mediated Endocytosis. Developmental cell 46 31353312
2021 Aagab acts as a novel regulator of NEDD4-1-mediated Pten nuclear translocation to promote neurological recovery following hypoxic-ischemic brain damage. Cell death and differentiation 20 33712741
2021 AAGAB is an assembly chaperone regulating AP1 and AP2 clathrin adaptors. Journal of cell science 17 34494650
2016 Eight Novel Mutations Confirm the Role of AAGAB in Punctate Palmoplantar Keratoderma Type 1 (Buschke-Fischer-Brauer) and Show Broad Phenotypic Variability. Acta dermato-venereologica 15 26608363
2024 An AAGAB-to-CCDC32 handover mechanism controls the assembly of the AP2 adaptor complex. Proceedings of the National Academy of Sciences of the United States of America 13 39145939
2022 The adaptor protein chaperone AAGAB stabilizes AP-4 complex subunits. Molecular biology of the cell 12 35976721
2019 AAGAB Mutations in 18 Canadian Families With Punctate Palmoplantar Keratoderma and a Possible Link to Cancer. Journal of cutaneous medicine and surgery 9 31526046
2013 Loss-of-function mutation in AAGAB in Chinese families with punctuate palmoplantar keratoderma. The British journal of dermatology 9 23448244
2013 A novel splice-site mutation in the AAGAB gene segregates with hereditary punctate palmoplantar keratoderma and congenital dysplasia of the hip in a large family. Clinical and experimental dermatology 9 24289292
2023 Oligomer-to-monomer transition underlies the chaperone function of AAGAB in AP1/AP2 assembly. Proceedings of the National Academy of Sciences of the United States of America 7 36598941
2024 Aagab is required for zebrafish larval development by regulating neural activity. Journal of genetics and genomics = Yi chuan xue bao 2 38253235
2017 Mutations in AAGAB underlie autosomal dominant punctate palmoplantar keratoderma. Clinical and experimental dermatology 2 28239884
2021 Only plantar lesion of punctate palmoplantar keratoderma with a novel missense mutation in the AAGAB gene: Two Japanese familial case reports and review of reported mutations. The Journal of dermatology 1 34535911
2025 Aagab-driven SHIP2 degradation rescues mitochondrial dysfunction in hypoxic-ischemic encephalopathy. Mitochondrion 0 41412220
2021 A novel AAGAB mutation in a Peruvian family with punctate palmoplantar keratoderma. Acta dermatovenerologica Alpina, Pannonica, et Adriatica 0 33765759

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