Structural and functional characterization of the Hsp90 molecular chaperone family
Maharaj, Kevin Amit
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Hsp90s are ATP-dependent molecular chaperones essential for the survival of all eukaryotic cells. They are among the most abundant proteins in the cell, consisting of over 2% of the total polypeptide mass and are key responders to a variety of stress signals which include heat shock, glucose deprivation, ATP and oxidative stress. In higher eukaryotes there are four hsp90 paralogs: cytosolic Hsp90α and Hsp90β, the heat inducible and constitutively expressed isoforms respectively; and two compartmentalized forms, GRP94, which is localized to the ER, and the mitochondrial paralog TRAP-1. Despite high structural and sequence homology between cytosolic Hsp90 and GRP94, there are dramatic structural and biochemical differences between the paralogs. The goal of these studies was to characterize the biochemical differences between members of the hsp90 family, relate these differences to structural elements of the chaperones, and from this gain insight into the mechanism of action of hsp90 chaperones. To this end, we employed a structure-function approach utilizing biophysical, biochemical and functional analyses to characterize the similarities and differences among hsp90 family members. Results indicated that hsp90 paralogs can functionally complement for one another and identified that in vitro ATP hydrolysis is not a reliable indicator of in vivo hsp90 functionality. Taken together this dissertation highlights the similarities and the differences between hsp90 paralogs.