htpG

Gene Description

HtpG is the bacterial member of the Hsp90 family of ATP-dependent molecular chaperones. It is a constitutive cytoplasmic homodimer built from three conserved domains per protomer: an N-terminal GHKL-type ATPase domain that binds and hydrolyzes ATP, a middle domain that contributes to ATP hydrolysis and engages the Hsp70 (DnaK) system, and a C-terminal dimerization domain that also contributes to client binding. HtpG functions in cellular protein quality control, binding non-native client proteins to prevent their aggregation (holdase activity) and, in collaboration with the Hsp70/DnaK chaperone system and its cochaperones, promoting client remodeling and refolding through an ATP-driven conformational cycle. Bacteria lack the extensive dedicated cochaperone network of eukaryotic Hsp90. In Pseudomonas putida KT2440, htpG (PP_4179) is a member of the heat-shock regulon: its transcription is rapidly and transiently induced by temperature upshift in a manner consistent with the alternative sigma factor RpoH (sigma-32), and it is further induced by osmotic and other physicochemical stresses, consistent with its role as a stress-responsive component of the cytosolic proteostasis network.

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005524 ATP binding	IEA GO_REF:0000120	ACCEPT	Summary: HtpG is a bacterial Hsp90-family chaperone with an N-terminal GHKL-type ATPase domain that binds ATP. ATP binding is a core, well-established feature of this family. Reason: Consistent with the conserved Hsp90/HtpG N-terminal ATP-binding domain and family-level evidence; ATP binding is essential for the chaperone's ATP-driven conformational cycle.
GO:0005737 cytoplasm	IEA GO_REF:0000120	ACCEPT	Summary: Bacterial HtpG is a soluble cytoplasmic chaperone acting on intracellular protein substrates. Reason: Consistent with UniProt subcellular location (Cytoplasm) and the known biology of cytosolic bacterial Hsp90; HtpG acts within the cytosolic proteostasis network.
GO:0006457 protein folding	IEA GO_REF:0000120	ACCEPT	Summary: As an Hsp90-family chaperone, HtpG participates in protein folding / quality control, binding non-native clients to prevent aggregation and assisting refolding in concert with the Hsp70/DnaK system. Reason: Core conserved biological process for the Hsp90/HtpG family, supported by family-level evidence and by stress-inducible expression in P. putida.
GO:0016887 ATP hydrolysis activity	IEA GO_REF:0000002	ACCEPT	Summary: The N-terminal/middle domains of HtpG constitute a GHKL ATPase that hydrolyzes ATP to drive the chaperone conformational cycle. Reason: ATPase activity is a defining catalytic feature of the Hsp90/HtpG family; UniProt also records ATPase activity for this protein.
GO:0140662 ATP-dependent protein folding chaperone	IEA GO_REF:0000002	ACCEPT	Summary: This term precisely captures HtpG's molecular function as an ATP-dependent chaperone that couples ATP binding/hydrolysis to the binding and folding/remodeling of client proteins. Reason: The most specific and accurate molecular-function term for an Hsp90-family chaperone; well supported by conserved family biology.

Core Functions

ATP-dependent molecular chaperone (bacterial Hsp90/HtpG) that binds non-native client proteins to prevent aggregation and, in collaboration with the Hsp70/DnaK system, promotes client remodeling and refolding.

Molecular Function:

ATP-dependent protein folding chaperone

Directly Involved In:

protein folding

Cellular Locations:

cytoplasm

Supporting Evidence:

PMID:38534118
Bacterial HtpG functions in protein quality control, binding non-native proteins and collaborating with the Hsp70/DnaK system to remodel and refold client proteins through an ATP-driven cycle.

ATP binding and hydrolysis by the N-terminal GHKL-type ATPase domain drives the conformational cycle required for chaperone activity.

Molecular Function:

ATP hydrolysis activity

Supporting Evidence:

PMID:38534118
HtpG has an N-terminal ATPase domain and undergoes an ATP-driven conformational cycle coupling nucleotide binding/hydrolysis to client handling.

As part of the heat-shock regulon, HtpG contributes to the cellular response to thermal and other environmental stresses by maintaining proteostasis.

Directly Involved In:

protein folding

Supporting Evidence:

PMID:25303383
In P. putida, htpG mRNA is heat-inducible within ~10 minutes of temperature upshift, correlating with RpoH/sigma-32 and consistent with a stress-adaptive protein quality control role.
file:PSEPK/htpG/htpG-deep-research-falcon.md
htpG/PP_4179 is a member of the P. putida KT2440 heat-shock regulon, induced by temperature upshift (RpoH/sigma-32), osmotic stress (10.1-fold), and elevated pressure, consistent with a stress-responsive proteostasis role.

Gene Description

Existing Annotations Review

Core Functions

ATP-dependent molecular chaperone (bacterial Hsp90/HtpG) that binds non-native client proteins to prevent aggregation and, in collaboration with the Hsp70/DnaK system, promotes client remodeling and refolding.

ATP binding and hydrolysis by the N-terminal GHKL-type ATPase domain drives the conformational cycle required for chaperone activity.

As part of the heat-shock regulon, HtpG contributes to the cellular response to thermal and other environmental stresses by maintaining proteostasis.

References

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