Elucidating the Mechanism of Substrate Recognition by the Bacterial Hsp90 Molecular Chaperone

•Bacterial Hsp90 middle and C-terminal domain flexibility is required for client recognition.•Bacterial Hsp90 causes local and long-range structural changes in a non-native client.•Bacterial Hsp90 can bind partially folded states that are transiently populated from the native ensemble.•We propose a general model of native client remodeling by Hsp90.

Hsp90 is a conformationally dynamic molecular chaperone known to promote the folding and activation of a broad array of protein substrates (“clients”). Hsp90 is believed to preferentially interact with partially folded substrates, and it has been hypothesized that the chaperone can significantly alter substrate structure as a mechanism to alter the substrate functional state. However, critically testing the mechanism of substrate recognition and remodeling by Hsp90 has been challenging. Using a partially folded protein as a model system, we find that the bacterial Hsp90 adapts its conformation to the substrate, forming a binding site that spans the middle and C-terminal domains of the chaperone. Cross-linking and NMR measurements indicate that Hsp90 binds to a large partially folded region of the substrate and significantly alters both its local and long-range structure. These findings implicate Hsp90's conformational dynamics in its ability to bind and remodel partially folded proteins. Moreover, native-state hydrogen exchange indicates that Hsp90 can also interact with partially folded states only transiently populated from within a thermodynamically stable, native-state ensemble. These results suggest a general mechanism by which Hsp90 can recognize and remodel native proteins by binding and remodeling partially folded states that are transiently sampled from within the native ensemble.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (53 K)Download as PowerPoint slide