Constantly updated knowledge of Hsp90.

Although protein folding, in principle is a spontaneous process which depends only upon the amino-acid sequence, the assistance of molecular chaperones is required for many proteins to achieve their final conformation in vivo. While Hsp90 is one of the major molecular chaperones, it has long been the most mysterious among them. Recent advances in our knowledge regarding Hsp90 structure and function, owing to both detailed biochemical and genetic characterizations of Hsp90 co-chaperones, as well as eminent structural studies have established Hsp90 as an ATPase-dependent chaperone, and have provided a paradigm of the Hsp90 chaperone cycle, which is sequentially tuned and coordinated by a variety of co-chaperones. Here we summarize the current knowledge regarding the structure and essential activities of Hsp90, which certainly promises a deeper understanding of the functions of Hsp90 in vivo.