Crystal structure of heat shock locus V (HslV) from Escherichia coli.

Heat shock locus V (HslV; also called ClpQ) is the proteolytic core of the ATP-dependent protease HslVU in Escherichia coli. It has sequence similarity with the beta-type subunits of the eukaryotic and archaebacterial proteasomes. Unlike these particles, which display 72-point symmetry, it is a dimer of hexamers with 62-point symmetry. The crystal structure of HslV at 3.8-A resolution, determined by isomorphous replacement and symmetry averaging, shows that in spite of the different symmetry of the particle, the fold and the contacts between subunits are conserved. A tripeptide aldehyde inhibitor, acetyl-Leu-Leu-norleucinal, binds to the N-terminal threonine residue of HslV, probably as a hemiacetal, relating HslV also functionally to the proteasomes of archaea and eukaryotes.