DNAJC24 (DnaJ homolog subfamily C member 24; also DPH4 / ZCSL3, Diphthamide biosynthesis protein 4) is a small cytoplasmic J-domain co-chaperone of the HSP70 system that also functions in diphthamide biosynthesis. It comprises an N-terminal J-domain (with the canonical HPD motif) and a C-terminal DPH-type CSL metal-binding domain that can coordinate either zinc or iron. Through its J-domain it stimulates the ATPase activity of HSP70-type chaperones; its CSL domain binds metal ions, and iron binding promotes oligomerization and confers redox/electron-carrier activity. DNAJC24 participates in the conserved multi-step diphthamide pathway that installs the diphthamide modification on a specific histidine of translation elongation factor 2 (EEF2), the residue targeted by diphtheria toxin and Pseudomonas exotoxin A.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001671 ATPase activator activity | IBA GO_REF:0000033 | ACCEPT | Summary: As a J-domain protein, DNAJC24/DPH4 stimulates the ATPase activity of HSP70-type chaperones. This phylogenetic inference is directly confirmed for the human protein. Reason: The J-domain of DPH4 catalytically stimulates HSP70 ATPase activity; this is the canonical molecular function of the gene, supported by both orthology and direct experimental evidence. Supporting Evidence: PMID:22367199 catalytically stimulate the ATPase activity of Hsp70 |
| GO:0008198 ferrous iron binding | IBA GO_REF:0000033 | ACCEPT | Summary: The CSL metal-binding domain of DPH4 binds iron (in addition to zinc), conferring redox/electron-carrier activity. Supported experimentally for the human protein. Reason: DPH4's CSL domain binds iron in solution (loss on the C139S mutation), a genuine molecular function corroborated by direct experimental evidence. Supporting Evidence: PMID:22367199 Dph4 possesses the intrinsic ability to bind iron in solution |
| GO:0005856 cytoskeleton | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Cytoplasm/cytoskeleton localization is annotated from the UniProt subcellular location (by similarity). The cytoskeletal association is weakly supported. Reason: The cytoplasm-cytoskeleton localization is by-similarity (ECO:0000250) rather than direct; DPH4 is a cytoplasmic co-chaperone, but cytoskeletal localization is not central to its characterized function. Supporting Evidence: file:human/DNAJC24/DNAJC24-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytoskeleton |
| GO:0015629 actin cytoskeleton | IEA GO_REF:0000107 | MARK AS OVER ANNOTATED | Summary: Actin-cytoskeleton localization transferred by orthology from the mouse protein. There is no direct human functional evidence linking DPH4 to the actin cytoskeleton. Reason: This is an Ensembl-Compara orthology transfer from mouse with no direct human evidence; DPH4's characterized roles are HSP70 co-chaperone and diphthamide biosynthesis, not actin-cytoskeleton activity. Supporting Evidence: file:human/DNAJC24/DNAJC24-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm, cytoskeleton |
| GO:0017183 protein histidyl modification to diphthamide | IEA GO_REF:0000120 | ACCEPT | Summary: DPH4 participates in the diphthamide biosynthesis pathway, a post-translational modification of a histidine in EEF2. This is the gene's defining biological process and is supported experimentally. Reason: DPH4 plays a documented role in diphthamide biosynthesis (the EEF2 histidine modification); this is the core biological process, supported by functional studies and pathway membership. Supporting Evidence: file:human/DNAJC24/DNAJC24-uniprot.txt Plays a role in the diphthamide biosynthesis, a post-translational modification of histidine which occurs in translation elongation factor 2 (EEF2) |
| GO:0001671 ATPase activator activity | IDA PMID:22367199 Structure and mechanistic insights into novel iron-mediated ... | ACCEPT | Summary: Direct experimental evidence that DPH4 stimulates the ATPase activity of HSP70-type chaperones. The core molecular function of the J-protein. Reason: IDA evidence that DPH4's J-domain stimulates HSP70 ATPase activity confirms its canonical co-chaperone molecular function. Supporting Evidence: PMID:22367199 catalytically stimulate the ATPase activity of Hsp70 |
| GO:0006457 protein folding | TAS PMID:22367199 Structure and mechanistic insights into novel iron-mediated ... | KEEP AS NON CORE | Summary: As an HSP70 co-chaperone, DPH4 is annotated to protein folding. This is a downstream process of the HSP70 machine it assists rather than autonomous foldase activity. Reason: DPH4 is a J-domain co-chaperone that delivers substrates to and stimulates HSP70; protein folding is a generic downstream process, non-core relative to its ATPase-activator function and diphthamide role. Supporting Evidence: PMID:22367199 The J-proteins sequester and deliver unfolded proteins to Hsp70 in the ATP-bound state |
| GO:0008198 ferrous iron binding | IDA PMID:22367199 Structure and mechanistic insights into novel iron-mediated ... | ACCEPT | Summary: Direct experimental evidence that DPH4 binds iron through its CSL domain, conferring redox properties. A genuine molecular function. Reason: IDA evidence (iron-binding lost in the C139S mutant) confirms DPH4 binds ferrous iron via its CSL metal-binding domain. Supporting Evidence: PMID:22367199 Dph4 possesses the intrinsic ability to bind iron in solution |
| GO:0008270 zinc ion binding | IDA PMID:22367199 Structure and mechanistic insights into novel iron-mediated ... | ACCEPT | Summary: Direct experimental and structural (NMR, PDB 2L6L) evidence that the CSL/DPH-type domain of DPH4 binds zinc ions via four conserved residues. Reason: IDA/structural evidence that the DPH-type metal-binding domain coordinates zinc confirms this molecular function; the domain can bind either zinc or iron. Supporting Evidence: file:human/DNAJC24/DNAJC24-uniprot.txt The DPH-type metal-binding (MB) domain can bind either zinc or iron ions. |
| GO:0032781 positive regulation of ATP-dependent activity | IDA PMID:22367199 Structure and mechanistic insights into novel iron-mediated ... | KEEP AS NON CORE | Summary: A process-level annotation reflecting DPH4's stimulation of HSP70 ATPase activity. Redundant with the more informative ATPase activator activity molecular function. Reason: This generic process term captures the same underlying activity as the ATPase activator activity MF; non-core because the MF term is more informative. Supporting Evidence: PMID:22367199 catalytically stimulate the ATPase activity of Hsp70 |
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Download this section (compressed HTML)Q: Which HSP70 paralog(s) does DPH4 stimulate in vivo, and is the J-domain co-chaperone activity required for diphthamide biosynthesis or separable from it?
Q: Is the iron-dependent redox/electron-carrier activity of DPH4 physiologically relevant to the radical-SAM chemistry of the diphthamide pathway (e.g. DPH1-DPH2)?
Experiment: Reconstitute the diphthamide pathway in vitro with DPH1-DPH7 and test whether DPH4 J-domain (HPD) mutants or iron-binding (C139S) mutants impair EEF2 diphthamide formation.
Experiment: Measure DPH4-stimulated ATPase activity of candidate HSP70 partners (HSPA8, HSPA9) and map which clients require DPH4 hand-off.
Experiment: Knockout DPH4 in cells and assay EEF2 diphthamidation and sensitivity to diphtheria toxin / Pseudomonas exotoxin A to confirm its in-vivo pathway role.
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