Hsp90 phosphorylation is linked to its chaperoning function - Assembly of the reovirus cell attachment protein

Studies on Hsp90 have mainly focused on its involvement in the activation o f several families of protein kinases and of steroid hormone receptors. Lit tle is known regarding the role of Hsp90 in the folding of nascent proteins . We previously reported that Hsp90 plays an active role in the posttransla tional assembly of the C-terminal globular head of the reovirus attachment protein sigma1. We show here that Hsp90 becomes phosphorylated in this proc ess. However, only the unphosphorylated form of Hsp90 is complexed with sig ma1, suggesting that Hsp90 phosphorylation is coupled to the release of the chaperone from the target protein. Geldanamycin, which blocks sigma1 matur ation by preventing the release of Hsp90 from sigma1, also inhibits Hsp90 p hosphorylation. Taken together, these results demonstrate that Hsp90 phosph orylation is linked to its chaperoning function.