Journal of Synchrotron Radiation

Volume 15, Part 3 (May 2008)

diffraction structural biology

J. Synchrotron Rad. (2008). 15, 246-249 [ doi:10.1107/S0909049507062826 ]

A degradation signal recognition in prokaryotes

E. Y. Park and H. K. Song

Abstract: The degradation of ssrA-tagged substrates in prokaryotes is conducted by a subset of ATP-dependent proteases, including ClpXP complex. More than 630 sequences of ssrA have been identified from 514 species, and are conserved in a wide range of prokaryotes. SspB protein markedly stimulates the degradation of these ssrA-tagged substrates by the ClpXP proteolytic machine. The dimeric SspB protein is composed of a compact ssrA-binding domain, which has a dimerization surface and a flexible C-terminal tail with a ClpX-binding motif at its very end. Since SspB is an adaptor protein for the ClpXP complex, designed mutagenesis, fluorescence spectroscopy, biochemistry and X-ray crystallography have been used to investigate the mechanism of delivery of ssrA-tagged proteins. In this paper the structural basis of ssrA-tag recognition by ClpX and SspB, as well as SspB-tail recognition by ZBD, is described.

Keywords: adaptor; ClpX; ClpXP complex; SspB; ssrA; zinc-binding domain.