Investigating Interactions Between the Hsp90 Molecular Chaperone and Unfolded Protein Substrates

Abstract

The ubiquitous protein chaperone Hsp90 plays an integral role in cellular homeostasis and protein folding by interacting with substrate proteins. Only recently have three-dimensional structures of the full-length Hsp90 been determined and a reaction cycle been proposed. Despite this achievement, remarkably little is known about the molecular basis for substrate interactions. To investigate this issue, I am utilizing a well-studied model of an unfolded protein, Δ131Δ, a fragment of staphylococcal nuclease. Using small angle x-ray scattering and structure-based fitting we have found that Hsp90 undergoes an open/closed conformational change in the presence of Δ131Δ. NMR measurements of Δ131Δ and domain fragments of Hsp90 have indicated the interaction location on both the chaperone and the substrate. We use this information to build a mechanistic model of how Hsp90 interacts with unfolded protein substrates and how different nucleotide states influence these interactions.