Regulation of the Hsp90 system.

Hsp90 is a highly conserved and abundant chaperone. It participates in essential cellular activities by supporting the maturation process of its client proteins, many of which are protein kinases and steroid receptors. Client processing is achieved via extensive conformational changes within the dimeric chaperone. This requires an ATP hydrolysis activity that is controlled by auto-inhibitory mechanisms and several structurally diverse cofactors. Especially the client-specificity of Hsp90 depends on client-specific cofactors, which can adapt Hsp90's activities to the client requirements at different conditions and in different cell types. Additionally, post-translational modifications can influence almost every aspect of Hsp90's interactions and activities. In this review, we present these regulatory principles, discuss the factors that have an impact on Hsp90's function and elaborate the mechanisms that are responsible for regulating the Hsp90 machinery.