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Related Experiment Video

Updated: Jul 5, 2026

Studies of Chaperone-Cochaperone Interactions using Homogenous Bead-Based Assay

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Published on: July 21, 2021

Structural studies on the co-chaperone Hop and its complexes with Hsp90.

S C Onuoha¹, E T Coulstock, J G Grossmann

¹Chemistry Department, Lensfield Road, University of Cambridge, Cambridge CB2 1EW, UK.

Journal of Molecular Biology

|May 20, 2008

Summary

The Hsp-organising protein (Hop) binds Heat Shock Protein 90 (Hsp90) at multiple sites, not just the C-terminus. This interaction, crucial for cellular assembly, forms a butterfly-like structure and influences Hsp90

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Published on: November 29, 2013

Area of Science:

Molecular Biology
Structural Biology
Biochemistry

Background:

The Hsp-organising protein (Hop) is a co-chaperone that bridges Heat Shock Protein 70 (Hsp70) and Hsp90.
Hop modulates the ATPase activity of Hsp70 and Hsp90, facilitating client protein transfer.
The full-length structure of Hop and its precise interaction with Hsp90 remain unclear, despite knowledge of its primary binding to the C-terminal MEEVD motif.

Purpose of the Study:

To elucidate the structural and binding characteristics of full-length Hop in complex with Hsp90.
To identify all binding sites of Hop on Hsp90 and understand Hop's role in Hsp90 dimerization.
To determine the quaternary structure of Hop and its nucleotide-dependent binding to Hsp90.

Main Methods:

Biophysical analysis using truncation mutants of Hop and Hsp90.
Analysis of Hsp90 mutants affecting its conformation and N-terminal dimerization.
Small-angle X-ray scattering (SAXS) for shape reconstruction.
Studies on nucleotide dependence of Hop-Hsp90 binding.

Main Results:

Hop binds Hsp90 at the C-terminal MEEVD motif and additional sites in the C-terminal and middle domains.
The TPR2a domain of Hop is critical for Hsp90 binding and dimerization, with potential involvement of TPR2b.
Full-length Hop adopts a butterfly-like quaternary structure in solution.
Hop binds the nucleotide-free, open state of Hsp90, and this interaction is weakened by ATP binding.

Conclusions:

Hop interacts with Hsp90 at multiple sites, forming a clamp-like structure that may regulate Hsp90 activity.
Hop's binding to Hsp90 likely involves presenting client proteins to Hsp90's middle domain.
The proposed model suggests Hop prevents ATP hydrolysis by inhibiting domain association within Hsp90 monomers.