Seth Harris

currently at Roche Pharmaceuticals

The 90 kilodalton heat shock protein (Hsp90) is a strongly conserved and ubiquitous molecular chaperone involved in a broad array of cellular functions. Hsp90 is unique among chaperones, however, due to its specific and fundamental role in cell signaling pathways. Our goal is to understand the mechanism of Hsp90 action and the structural basis for its requirement by substrate proteins.

Hsp90 is characterized by an ATP-binding amino-terminal domain, a relatively flexible middle domain, and a carboxy-terminal dimerization domain. Crystal structures have been solved for amino-terminal fragments of yeast and human Hsp90’s bound to ATP, ADP or the anti-cancer drug geldanamycin, and more recently the yeast Hsp90 middle domain has also been solved, but such fragments cannot describe the extensive inter-domain communication inherent in Hsp90 function. By X-ray crystallography, we have produced a medium resolution map of the complete E. coli Hsp90 homologue, high temperature protein G (htpG), delineating the overall pincer-like architecture of the chaperone dimer. These data support our model that Hsp90 proteins act as twisting pincers that clamp around sub-domains or partially folded segments of client proteins. The moderate diffraction, fragility, and large unit cell of our crystals has until now thwarted completion of the htpG model. We have now solved high resolution structures for each of the three primary htpG domains and these can be docked back into the maps of the full length protein. As we refine this model it show us the first view of a complete, intact Hsp90 molecule, a cohesive picture that has been lacking from the independent domain structures solved to date. We are discovering structural features, such as exposed amphipathic helices near the carboxy-terminal dimerization domain that I recently solved, that will help our continuing efforts to understand substrate binding, co-chaperone interactions, and the important conformational changes that the protein must use to connect nucleotide binding, hydrolysis, and release to substrate interaction as it completes its chaperone cycle.

Additionally, I have been developing various computational database tools to track and help organize and automate crystallization trials and a comprehensive laboratory notebook system.