P58IPK (CG8286, dIPK) is the single Drosophila member of the DNAJC3/P58IPK family of J-domain cochaperones and is the ortholog of vertebrate DNAJC3. The 498-residue protein has an N-terminal signal peptide, an array of tetratricopeptide (TPR) repeats, and a C-terminal J domain with a conserved HPD motif (H424). By descent from the ancestral family function, it is expected to enter the endoplasmic reticulum, bind misfolded client proteins through its TPR region, and use its J domain to engage the ER Hsp70 chaperone BiP (Hsc70-3) and hand clients over for folding. Direct experiments on the fly protein are limited to overexpression studies, in which it co-immunoprecipitated with polyglutamine-expanded huntingtin (HTT103Q) and reduced its aggregation in yeast, S2 cells and larval hemocytes. Its endogenous localization, clients and Hsp70 partner have not been determined, and the eIF2-alpha kinase inhibitory activity described for mammalian DNAJC3 has not been shown for the fly protein.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: ER localization is inherited from the eukaryote-level PAINT node and fits the signal-peptide J/TPR architecture. Reason: The IBD sits on the Eukaryota root node PTN001941043, from which the fly gene descends through the Bilateria node shared with vertebrate DNAJC3; it is seeded by mouse Dnajc3, yeast JEM1 and fungal DNJ1 experimental data. Mouse P58/DNAJC3 is mostly translocated into the ER lumen, and Q9VHA8 has an N-terminal signal peptide. The more specific ER lumen is likely for the fly protein but not shown, and the PAINT curators placed the general ER term (JEM1 is membrane-associated), so ER is kept as the appropriate precision. Supporting Evidence: file:DROME/P58IPK/P58IPK-bioinformatics/RESULTS-rereview.md fly P58IPK and human DNAJC3 are orthologs, joined by the Bilateria speciation node PTN000637047 PMID:18923430 Most P58 molecules are translocated into the ER lumen file:DROME/P58IPK/P58IPK-uniprot.txt FT SIGNAL 1..36 |
| GO:0005783 endoplasmic reticulum | IEA GO_REF:0000044 | ACCEPT | Summary: Same ER claim as the IBA row; consistent with orthology and the signal peptide. Reason: The UniProt subcellular-location line behind this mapping is an ARBA rule and is not itself used as support. The claim is nonetheless correct, supported by the PAINT placement and the signal peptide, and is kept consistent with the IBA row for the same term. Supporting Evidence: PMID:18923430 Most P58 molecules are translocated into the ER lumen file:DROME/P58IPK/P58IPK-uniprot.txt FT SIGNAL 1..36 |
| GO:0012505 endomembrane system | HDA PMID:19317464 Mapping organelle proteins and protein complexes in Drosophi... | KEEP AS NON CORE | Summary: High-throughput organelle proteomics placed the protein in the endomembrane fraction, consistent with ER residence. Reason: PMID:19317464 is an organelle-mapping proteomics study (abstract-only in the cache). The FlyBase HDA assignment is as precise as the high-throughput evidence allows and is compatible with the ER localization captured by the IBA row. It is retained as corroborating, non-core localization evidence; it does not establish membrane insertion, and the protein has no predicted transmembrane segment beyond the signal peptide. Supporting Evidence: file:DROME/P58IPK/P58IPK-uniprot.txt FT SIGNAL 1..36 |
| GO:0034975 protein folding in endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: ER protein folding is the ancestral family role, inherited from the Eukaryota node. Reason: The cochaperone itself does part of the work of the process, capturing misfolded clients through its TPR region and coupling their release to BiP via its J domain. The mouse ortholog shows this directly, and the fly protein retains the HPD histidine (H424) corresponding to the P58 H422 required for the BiP interaction. The node is placed at Eukaryota by PAINT and the fly gene shows no sign of loss of the J domain or TPR array. Supporting Evidence: PMID:18923430 These findings are consistent with a model whereby localized activation of the Hsp70-type partner is sufficient to promote substrate handover from the J-domain co-chaperone. file:DROME/P58IPK/P58IPK-bioinformatics/RESULTS-rereview.md The J-domain HPD tripeptide of Q9VHA8 is at residues 424-426 file:DROME/P58IPK/P58IPK-bioinformatics/RESULTS-rereview.md The PAINT IBD assertions are all placed at the Eukaryota root node PTN001941043 |
| GO:0051087 protein-folding chaperone binding | IBA GO_REF:0000033 | ACCEPT | Summary: J-domain-mediated binding to the ER Hsp70 BiP is the core cochaperone activity. Reason: In mouse P58/DNAJC3, the J domain interacts with BiP through the invariant HPD histidine H422, and BiP plus ATP drives client release. Q9VHA8 conserves the HPD motif (H424) within its J domain, and the activity is inherited from the eukaryote root PAINT node. The fly Hsp70 partner (presumably Hsc70-3/BiP) is not experimentally identified. Supporting Evidence: PMID:18923430 BiP-induced dissociation of P58 from its substrate depends on the presence of ATP and on interactions with P58's J-domain, which are mediated by invariant residues BiP R197 and P58 H422 file:DROME/P58IPK/P58IPK-bioinformatics/RESULTS-rereview.md The J-domain HPD tripeptide of Q9VHA8 is at residues 424-426 |
| GO:0051787 misfolded protein binding | IBA GO_REF:0000033 | ACCEPT | Summary: TPR-mediated binding of misfolded clients is the ancestral family activity, with supporting fly-protein data. Reason: Mouse P58 binds misfolded proteins selectively and stably through its TPR-containing N-terminal region, which is the donor evidence for the PAINT node. For the fly protein, HA-tagged P58IPK co-immunoprecipitated with aggregation-prone HTT103Q-GFP in yeast, consistent with misfolded-client binding, though this does not prove direct binding and the client is artificial. Supporting Evidence: PMID:18923430 here we report selective and stable binding to misfolded proteins by P58's TPR-containing N-terminal domain PMID:39242711 HA bands were seen in the input and IP lanes of mutant 103Q with CG5001 and P58IPK whereas the negative controls show no bands in the IP |
Loading supporting content…
Download this section (compressed HTML)Q: Is endogenous fly P58IPK ER-luminal, as its signal peptide and the mammalian ortholog suggest, and how does an overexpressed signal-peptide protein colocalize with cytoplasmic HTT103Q aggregates?
Q: Does fly P58IPK inhibit PEK (fly PERK) or GCN2 as mammalian DNAJC3 inhibits eIF2-alpha kinases, or is the kinase-inhibitory role a vertebrate-lineage addition? PAINT did not propagate it to any ancestral node.
Q: Is fly P58IPK induced by ER stress (Ire1/Xbp1 or Atf6 dependent) as DNAJC3 is in mammals?
Experiment: Endogenous tagging (CRISPR knock-in) of P58IPK with ER-lumen and cytosol markers and protease-protection assays to establish its topology and compartment.
Experiment: Purified P58IPK with Hsc70-3 (BiP) in ATPase stimulation and client-release assays, comparing wild type with an H424Q J-domain mutant.
Experiment: P58IPK null alleles assayed for ER stress sensitivity, eIF2-alpha phosphorylation and PEK epistasis.
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)