Chrisostomos Prodromou

Structural basis for recruitment of the ATPase activator Aha1 to the Hsp90 chaperone machinery (vol 23, pg 511, 2004)

Hsp90 is a molecular chaperone essential for the activation and assembly of many key eukaryotic signalling and regulatory proteins. Hsp90 is assisted and regulated by co-chaperones that participate in an ordered series of dynamic multiprotein complexes, linked to Hsp90 conformationally coupled ATPase cycle. The co-chaperones Aha1 and Hch1 bind to Hsp90 and stimulate its ATPase activity. Biochemical analysis shows that this activity is dependent on the N-terminal domain of Aha1, which interacts with the central segment of Hsp90. The structural basis for this interaction is revealed by the crystal structure of the N-terminal domain (1-153) of Aha1 (equivalent to the whole of Hch1) in complex with the middle segment of Hsp90 (273-530). Structural analysis and mutagenesis show that binding of N-Aha1 promotes a conformational switch in the middle-segment catalytic loop (370-390) of Hsp90 that releases the catalytic Arg 380 and enables its interaction with ATP in the N-terminal nucleotide-binding domain of the chaperone.

CHAPTER 2:Structural Basis of Hsp90 Function

Heat shock protein 90 (Hsp90) stands at the crossroads of many signaling pathways responsible for cell proliferation, differentiation, cell homeostasis and apoptosis. Consequently, it is no surprise that Hsp90 is associated with all the six hallmarks of cancer and has become a prime anticancer target. Central to the Hsp90 mechanism is its ATPase activity, which is coupled to a conformational cycle involving a complex set of structural changes that involve all Hsp90 domains. The mechanism by which Hsp90 activates “client” protein is still poorly understood. However, there has been excellent progress on elucidating the molecular details of the complex structural changes required for Hsp90’s catalytically active state and how this activity is influenced by a variety of co-chaperones and client proteins. This review aims to bring together structural investigations that have so far contributed to our understanding of this ATPase-coupled conformational cycle and how this activity is regulated and ultimately has become the prime target for Hsp90 drugs.