Crystal and solution structures of an HsIUV protease-chaperone complex

HslUV is a prokaryotic proteasome composed of the HslV protease and the HslU ATPase, a chaperone of the Clp/Hsp100 family. The 3.4 a crystal structure of an HslUV complex is presented here. Two hexameric ATP binding rings of HslU bind intimately to opposite sides of the HslV protease; the HslU intermediate domains extend outward from the complex. The solution structure of HslUV, derived from small angle X-ray scattering data under conditions where the complex is assembled and active, agrees with this crystallographic structure. When the complex forms, the carboxy-terminal helices of HslU distend and bind between subunits of HslV, and the apical helices of HsIV shift substantially, transmitting a conformational change to the active site region of the protease.