DNAJC27 (RBJ/RABJS; "Rab and DnaJ domain-containing protein") is an unusual chimeric protein combining an N-terminal Ras/Rab-like small-GTPase (P-loop NTPase) domain with a C-terminal DnaJ/J domain, a member of the RJL family. It binds GTP and, in its GTP-bound form, engages the MAP kinase MAP2K1/MEK1 and binds MAPK1/ERK2 through its N-terminal region; nucleus-localized RBJ entraps MEK1/MEK2 in the nucleus and prolongs ERK1/ERK2 activation, acting as a positive regulator/scaffold of the MEK/ERK (MAPK) cascade. Unlike canonical Ras-superfamily GTPases the RJL proteins lack the catalytic glutamine that coordinates GTP hydrolysis, so its intrinsic GTPase activity is uncertain. The C-terminal J domain is predicted to recruit Hsc70/HSP70. DNAJC27 is enhanced in testis, is overexpressed in gastrointestinal cancers, and behaves as an oncogene promoting carcinogenesis and tumor progression.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0003924 GTPase activity | IEA GO_REF:0000120 | MARK AS OVER ANNOTATED | Summary: Electronic/IBA assignment of GTPase activity from the Ras-superfamily domain. However, RJL-family proteins lack the conserved catalytic glutamine required for GTP hydrolysis, and UniProt notes a possible lack of GTPase activity, so catalytic turnover is doubtful for DNAJC27. Reason: The defining catalytic glutamine of Ras-superfamily GTPases is absent in RJL proteins; GTP binding is supported but hydrolytic GTPase activity is unproven and likely absent. Supporting Evidence: PMID:14980719 RJLs lack classical membrane targeting signals and the conserved glutamine residue that coordinates GTP hydrolysis in other proteins from the Ras superfamily. |
| GO:0005525 GTP binding | IEA GO_REF:0000002 | ACCEPT | Summary: GTP binding inferred from the conserved P-loop and GTP-binding motifs of the N-terminal Ras/Rab-like domain. The UniProt entry annotates explicit GTP-binding sites. Reason: The N-terminal domain has intact GTP-binding motifs (P-loop) and is classified in the small-GTPase/Rab family; GTP binding is well supported even though hydrolysis is doubtful. Supporting Evidence: file:human/DNAJC27/DNAJC27-uniprot.txt BINDING 23..30 |
| GO:0005634 nucleus | IEA GO_REF:0000120 | ACCEPT | Summary: Nuclear localization, consistent with the functionally important nuclear pool of RBJ that entraps MEK1/MEK2 and prolongs ERK activation. Reason: Nucleus is the functionally relevant compartment for RBJ's MEK/ERK scaffold activity; supported by the ISS annotation and by the experimental nuclear-entrapment mechanism. Supporting Evidence: file:human/DNAJC27/DNAJC27-uniprot.txt SUBCELLULAR LOCATION: Nucleus |
| GO:0031410 cytoplasmic vesicle | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: ARBA rule-based prediction of cytoplasmic vesicle localization, likely transferred from generic Rab-family membership. Not supported by the documented nuclear localization or function of DNAJC27. Reason: Generic Rab-family vesicle association predicted by a machine-learning rule; conflicts with the established nuclear localization and is unsupported by experimental data for this protein. Supporting Evidence: PMID:14980719 RJLs lack classical membrane targeting signals |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | KEEP AS NON CORE | Summary: Large-scale yeast two-hybrid interactome screen capturing a DNAJC27-TFCP2 interaction. The bare protein binding term is uninformative and not clearly related to RBJ's MEK/ERK function. Reason: Records a real high-throughput binary interaction (with TFCP2) but bare protein binding is uninformative and not elevated to core. Supporting Evidence: file:human/DNAJC27/DNAJC27-uniprot.txt Q9NZQ0; Q12800: TFCP2; NbExp=6; IntAct=EBI-10317544, EBI-717422 |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | KEEP AS NON CORE | Summary: Binary HuRI interactome screen again capturing the DNAJC27-TFCP2 interaction. Bare protein binding, uninformative. Reason: Corroborates the TFCP2 interaction from a second high-throughput map but remains an uninformative bare-binding annotation. Supporting Evidence: file:human/DNAJC27/DNAJC27-uniprot.txt Q9NZQ0; Q12800: TFCP2; NbExp=6; IntAct=EBI-10317544, EBI-717422 |
| GO:0070374 positive regulation of ERK1 and ERK2 cascade | IEA GO_REF:0000107 | ACCEPT | Summary: DNAJC27/RBJ positively regulates the ERK1/ERK2 cascade by interacting with MEK1/MEK2 and prolonging the duration of MEK/ERK activation; loss of Rbj attenuates ERK1/2 activation. This is the best-characterized function. Reason: Strongly supported by the mechanistic study (nuclear entrapment of MEK1/MEK2, prolonged ERK activation, oncogenic transformation) and by the UniProt FUNCTION statement; represents the core biological role. Supporting Evidence: PMID:24746703 Nucleus-localized RBJ interacts with MEK/ERK and prolongs the duration of MEK/ERK activation. |
| GO:0005634 nucleus | ISS GO_REF:0000024 | ACCEPT | Summary: Sequence/orthology-based nuclear localization (from mouse Q8CFP6), consistent with the functional nuclear pool of RBJ. Reason: Nucleus is the functionally relevant site of RBJ's MEK/ERK scaffold activity. Supporting Evidence: file:human/DNAJC27/DNAJC27-uniprot.txt SUBCELLULAR LOCATION: Nucleus |
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Download this section (compressed HTML)Q: Does human DNAJC27 retain any catalytic GTPase activity despite lacking the canonical catalytic glutamine, or does it function purely as a GTP-loaded conformational switch/scaffold?
Q: Is the C-terminal J domain of DNAJC27 a functional Hsc70/HSP70 co-chaperone (stimulating ATPase activity), and does Hsc70 recruitment contribute to MEK/ERK scaffolding?
Experiment: Recombinant GTP-hydrolysis and nucleotide-exchange assays on the DNAJC27 GTPase domain (wild-type vs catalytic-residue mutants) to determine whether it hydrolyzes GTP.
Experiment: J-domain HSP70 ATPase-stimulation assay and HPD-motif mutagenesis to test whether DNAJC27 acts as a bona fide Hsc70 co-chaperone.
Experiment: Domain-dissection co-immunoprecipitation and live-cell imaging to map which RBJ domain mediates nuclear MEK1/MEK2 entrapment and to test the GTP-dependence of the MEK/ERK interactions.
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