Contribution of N- and C-terminal domains to the function of Hsp90 in Saccharomyces cerevisiae

The molecular chaperone Hsp90 is a regulatory component of some key signall ing proteins in the cytosol of eukaryotic cells. For some of these function s, its interaction with co-chaperones is required. Limited proteolysis defi ned stable folded units of Hsp90. Both an N-terminal (N210) and a C-termina l (262C) fragment interact with non-native substrate proteins in vitro, but with different specificity and ATP dependence. Here, we analysed the funct ional properties of these Hsp90 fragments in vivo and in vitro. We determin ed their influence on the general viability and cell growth of Saccharomyce s cerevisiae. Expression of N210 or 262C resulted in a dominant-negative ph enotype in several yeast strains tested. Their expression was not toxic, bu t inhibited cell growth. Further, both were unable to restore viability to Hsp90-depleted cells. In addition, N210 and 262C influence the maturation o f Hsp90 substrates, such as the glucocorticoid receptor and pp60(v-Src) kin ase. Specifically, 262C forms partially active chaperone complexes, leading to an arrest of the chaperoned substrate at a certain stage of its maturat ion cycle. This demonstrates the requirement of a sophisticated and cofacto r-regulated interplay between N- and C-terminal activities for Hsp90 functi on in vivo.