The Hsp90 Chaperone: H and F Dynamic Nuclear Magnetic Resonance Spectroscopy Reveals a Perfect Enzyme.

Hsp90 is a crucial chaperone whose ATPase activity is fundamental for stabilizing and activating a diverse array of client proteins. Binding and hydrolysis of ATP by dimeric Hsp90 drive a conformational cycle characterized by fluctuations between a compact， N- and C-terminally dimerized catalytically competent closed state and a less compact open state that is largely C-terminally dimerized. We used F and H dynamic nuclear magnetic resonance (NMR) spectroscopy to study the opening and closing kinetics of Hsp90 and to determine the k for ATP hydrolysis. We derived a set of coupled ordinary differential equations describing the rate laws for the Hsp90 kinetic cycle and used these to analyze the NMR data. We found that the kinetics of closing and opening for the chaperone are slow and that the lower limit for k of ATP hydrolysis is ∼1 s. Our results show that the chemical step is optimized and that Hsp90 is indeed a "perfect" enzyme.