GrpE is the bacterial nucleotide exchange factor (NEF) for the Hsp70 chaperone DnaK, functioning as the third component of the conserved DnaK/DnaJ/GrpE (KJE) chaperone system. It is a homodimeric, "cruciform"-shaped protein with a long N-terminal coiled-coil and a globular C-terminal head domain that docks onto the nucleotide-binding domain (NBD) of DnaK. In the chaperone cycle, unfolded substrate proteins are first bound by DnaJ (Hsp40), which delivers them to DnaK and stimulates ATP hydrolysis to produce the ADP-bound, high substrate-affinity state of DnaK. GrpE then binds the DnaK NBD and induces conformational opening of the nucleotide-binding cleft (notably rotation of NBD subdomain IIB), accelerating ADP release; subsequent ATP rebinding resets DnaK to its low-affinity state and triggers substrate release, completing the cycle. Through this activity GrpE enables the iterative ATP-driven cycles required for de novo protein folding, refolding of stress-denatured proteins, and prevention of protein aggregation. The thermolabile coiled-coil of GrpE has been proposed to act as a thermosensor that modulates NEF activity with temperature. GrpE acts in the cytoplasm/cytosol and is part of the heat-shock and general stress response; in P. putida KT2440 it is induced under heat and chemical (e.g. phenol/solvent) stress.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000774 adenyl-nucleotide exchange factor activity | IEA GO_REF:0000120 | ACCEPT | Summary: This is the defining molecular function of GrpE - it is the nucleotide exchange factor for DnaK (Hsp70), promoting ADP release so that ATP can rebind. The annotation is from InterPro (IPR000740, the GrpE family signature) plus PANTHER and is fully consistent with the UniProt FUNCTION statement and the entire GrpE literature. Reason: Core, defining molecular function of GrpE. Universally conserved across the GrpE family and well supported by the InterPro/HAMAP family signature and mechanistic structural studies of bacterial DnaK-GrpE complexes. |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: GrpE acts in the cytoplasm as a cofactor of the cytosolic DnaK chaperone. The UniProt SUBCELLULAR LOCATION (HAMAP MF_01151) annotates Cytoplasm, and KT2440 proteomics detected GrpE among cytoplasmic stress-induced proteins. Reason: Correct subcellular localization for a bacterial DnaK cofactor. Consistent with HAMAP rule and with the cytosolic localization of its DnaK/DnaJ partners. |
| GO:0005829 cytosol | IEA GO_REF:0000118 | ACCEPT | Summary: TreeGrafter (phylogenetic) annotation to cytosol, the more specific child of cytoplasm. Consistent with GrpE function as a soluble cofactor of cytosolic DnaK. Reason: Correct and slightly more specific localization than the cytoplasm annotation. Both are biologically appropriate for GrpE; retaining the more specific cytosol term is reasonable. |
| GO:0006457 protein folding | IEA GO_REF:0000002 | ACCEPT | Summary: GrpE is an integral component of the DnaK/DnaJ/GrpE chaperone machine, which assists de novo protein folding and refolding of stress-denatured proteins. Several rounds of GrpE-driven nucleotide exchange are required for efficient folding. InterPro-based annotation is well supported. Reason: Accurately captures the biological process in which GrpE participates. GrpE is not itself a foldase but is essential to the folding cycle of the KJE system. |
| GO:0042803 protein homodimerization activity | IEA GO_REF:0000002 | ACCEPT | Summary: GrpE functions as a homodimer; dimerization (via the coiled-coil) is essential for its NEF activity and for engaging DnaK in the asymmetric 1:2 DnaK:GrpE complex. UniProt SUBUNIT annotates Homodimer. Well supported by InterPro and structural studies. Reason: GrpE is obligately dimeric and dimerization is required for function. Correct molecular function annotation. |
| GO:0051087 protein-folding chaperone binding | IEA GO_REF:0000002 | ACCEPT | Summary: GrpE binds directly to the Hsp70 chaperone DnaK (a protein-folding chaperone), docking onto its nucleotide-binding domain. This binding is the basis of its NEF activity. InterPro-based annotation is appropriate and more informative than generic protein binding. Reason: GrpE's physical interaction with the DnaK chaperone is central to its function. The term correctly describes this binding to a folding chaperone rather than an uninformative generic protein binding term. |
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Download this section (compressed HTML)Q: Does the proposed thermosensor behavior of the GrpE coiled-coil operate at physiologically relevant temperatures for P. putida, given its mesophilic environmental lifestyle?
Experiment: Determine the operon structure and promoter(s) of the grpE-dnaK-dnaJ locus (PP_4728 region) in P. putida KT2440 (e.g. by RNA-seq/transcription start site mapping and co-transcription assays) to confirm the inferred Pseudomonas chaperone gene cluster organization.
Experiment: Test whether a grpE conditional/depletion mutant in KT2440 impairs growth and protein refolding under heat and solvent (phenol) stress, to directly link the NEF function to stress-tolerance phenotypes in this organism.
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