Functional and Structural Characterization of Helicobacter pylori ClpX: A Molecular Chaperone of Hsp100 Family

ClpX is a general stress protein which belongs to the heat shock protein, Clp/Hsp100 family of molecular chaperones. ClpX, in association with ClpP degrades proteins in an ATP dependent manner. Some members of the Clp family have been shown to be involved in the pathogenesis of many bacteria. The Helicobacter pylori genome demonstrates the presence of ClpX along with ClpA, ClpB and ClpP, the other members of the caseinolytic protease family. H. pylori ClpX is a 386 amino acid long protein. In this study, we have over-expressed H. pylori ClpX in E. coli, purified the recombinant protein to homogeneity and functionally characterized it. The recombinant H. pylori ClpX showed an inherent ATPase activity and prevented the heat induced aggregation of a model protein in vitro. The chaperonic activity of H. pylori ClpX was dependent on ATP hydrolysis and involved hydrophobic interaction with the substrate protein. Biophysical studies reveal the secondary structure tolerance of ClpX at various temperatures and in the presence of guanidine hydrochloride. The study demonstrates that H. pylori ClpX manifests chaperonic activity in the absence of any adaptor protein.