htpG

htpG is a bacterial gene encoding HtpG, the cytosolic member of the Hsp90 family of molecular chaperones. As an ATP-dependent chaperone, HtpG assists in the folding, stabilization, and reconfirmation of protein clients, particularly under stress conditions such as elevated temperatures. The protein typically functions as a homodimer and is composed of three domains: an N-terminal ATPase domain, a middle client-binding domain, and a C-terminal dimerization domain. Unlike many eukaryotic cytosolic Hsp90s, bacterial HtpG generally lacks the MEEVD motif found at the extreme C-terminus.

Expression of htpG is part of the bacterial heat shock response. In Escherichia coli and many other bacteria, transcription is upregulated during stress by the heat shock sigma factor, often referred to as RpoH, aligning HtpG production with other chaperone systems.

Functionally, HtpG participates in maintaining proteostasis by assisting in the correct folding or stabilization of diverse substrate proteins during stress. It frequently operates in concert with the DnaK-DnaJ-GrpE (Hsp70) chaperone system and can interact with the GroEL/GroES machinery in some cellular contexts. While not essential for viability under standard laboratory conditions, HtpG contributes to thermotolerance and stress resilience, with its importance varying among bacterial species.

In research, htpG has served as a model for studying the interplay between Hsp90-family chaperones and other proteostasis networks, highlighting its role as a backup or supportive chaperone during heat stress. Overall, htpG encodes a bacterial Hsp90 homolog that helps preserve protein homeostasis under challenging conditions.