Structural basis for inhibition of the Hsp90 molecular chaperone by the antitumor antibiotics radicicol and geldanamycin

The cellular activity of several regulatory and signal transduction protein s, which depend on the Hsp90 molecular chaperone for folding, is markedly d ecreased by geldanamycin and by radicicol (monorden). We now show that thes e unrelated compounds both bind to the N-terminal ATP/ADP-binding domain of Hsp90, with radicicol displaying nanomolar affinity, and both inhibit the inherent ATPase activity of Hsp90 which is essential for its function in vi vo. Crystal structure determinations of Hsp90 N-terminal domain complexes w ith geldanamycin and radicicol identify key aspects of their nucleotide mim icry and suggest a rational basis for the design of novel antichaperone dru gs.