Disruption of zebrafish cyclin G-associated kinase (GAK) function impairs the expression of Notch-dependent genes during neurogenesis and causes defects in neuronal development.
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Zebrafish has two auxilin-family genes, gak (with an N-terminal kinase domain) and auxilin/dnajc6 (PTEN region, clathrin-binding motif and J domain, no kinase); zAux is more similar to human and mouse auxilin than to zGAK.
"zAux is similar to zGAK, it is more similar to human and mouse auxilin proteins (Figure 2A), suggesting that the divergence of GAK and auxilin occurred prior to the divergence of fish and mammals during vertebrate evolution."
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GFP-zAux and GFP-zGAK expressed at low levels in HeLa cells are mostly cytosolic with perinuclear enrichment overlapping clathrin (probably TGN); at high levels both form large clathrin-containing aggregates.
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Both GFP-zAux and GFP-zGAK rescue the extra photoreceptor (Elav-positive cell) phenotype and the lethality of Drosophila auxilin (dAux) mutants; J-domain-deleted versions of either do not.
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zAux is expressed maternally and zygotically, predominantly in neural tissues: bilateral dorsal cell clusters, hindbrain and spinal cord neurons, and otic vesicles; gak is broadly expressed.
Role of auxilin in uncoating clathrin-coated vesicles.
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Auxilin (bovine auxilin 1, the ortholog of zebrafish dnajc6) is the 100K cofactor of hsp70c in clathrin uncoating; it binds assembled clathrin lattices with high affinity, recruits hsp70c in the presence of ATP, and requires its C-terminal J domain for cofactor activity.
Structure of the PTEN-like region of auxilin, a detector of clathrin-coated vesicle budding.
Endocytosis and clathrin-uncoating defects at synapses of auxilin knockout mice.
UniProt entry A0A8M9QG43 (dnajc6, Danio rerio)
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Unreviewed (PE 4) entry, 974 aa, RefSeq XP_021332835.1. PROSITE predicts a tensin-type phosphatase domain (109-276), a tensin-type C2 domain (282-417) and a J domain (910-974) containing the HPD motif. The SUBUNIT and SUBCELLULAR LOCATION comments are ARBA transfers and are not used as evidence in this review.
UniProt entry O75061 (DNAJC6, Homo sapiens)
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Human auxilin is a reviewed entry whose phosphatase activity is hedged ("May act as a protein phosphatase and/or a lipid phosphatase", EC 3.1.3.-), while its co-chaperone role in recruiting HSPA8 to clathrin-coated vesicles and stimulating HSPA8 ATP hydrolysis is described in detail with curated evidence.
PAINT ancestral annotations for PANTHER family PTHR23172
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Root node PTN000571055 (Eukaryota) carries IBD clathrin binding, clathrin coat disassembly, vesicle, cytoplasm and intracellular membrane-bounded organelle; vertebrate node PTN002753975 (Euteleostomi) carries synaptic vesicle uncoating and postsynaptic density. No phosphatase activity is asserted at any node.
dnajc6 isoform and motif comparison (re-review)
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A0A8M9QG43 differs from the gene-centric canonical A0A8M9Q6X2 only by a 5-residue N-terminal deletion (GPPSP after residue 66), outside all domains; the HPD motif is retained, and the predicted catalytic cysteine sits in a CX3R window (CSDGR) like human auxilin (CLDGR) rather than a PTEN-class CX5R P loop.
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Electronic Gene Ontology annotations created by transferring manual GO annotations between related proteins based on shared sequence features
Deep research report for dnajc6 (A0A8M9QG43) in Danio rerio
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Auxilin/DNAJC6 is a J-domain co-chaperone that recruits and activates HSC70 to catalyse ATP-dependent disassembly of clathrin coats at the terminal step of clathrin-mediated endocytosis, supporting synaptic vesicle recycling.
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The PTEN-like domain binds phosphoinositides to target auxilin to endocytic membranes; it is not described as catalytically active.
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Biallelic loss-of-function DNAJC6 variants cause PARK19 juvenile-onset parkinsonism; the report notes that zebrafish-specific functional studies of dnajc6 are lacking.