Structural Analysis of E. coli hsp90 reveals dramatic nucleotide-dependent conformational rearrangements

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Heat-shock proteins (Hsp90) are vital molecular chaperones in eukaryotes, essential for protein folding, signaling, proliferation, and survival.
• HtpG from Escherichia coli is the ortholog of the Hsp90 chaperone family.

Purpose of the Study:

• To investigate the structural impact of nucleotide binding on the Hsp90 ortholog, HtpG.
• To elucidate the mechanism by which nucleotides regulate HtpG conformation and client protein interactions.

Main Methods:

• Electron microscopy (EM) was employed to visualize HtpG structures.
• X-ray crystallography was used for higher-resolution structural characterization of nucleotide-free and ADP-bound HtpG.

Main Results:

• Nucleotide-free, AMPPNP-bound, and ADP-bound states of HtpG exhibit distinct conformations.
• Nucleotide-free HtpG adopts an "open" conformation with exposed hydrophobic elements.
• ADP binding induces significant conformational changes, shielding hydrophobic elements and suggesting a regulatory mechanism.

Conclusions:

• Nucleotide binding acts as a critical switch, controlling HtpG conformation.
• The conformational changes driven by ADP binding are key to regulating client protein association and dissociation.
• Understanding HtpG's nucleotide-dependent structural dynamics provides insights into Hsp90 chaperone function.