Intramolecular chaperone activity of the pro-region of Vibrio cholerae El Tor cytolysin.

Vibrio cholerae synthesizes a toxin named El Tor cytolysin/hemolysin, which lyses erythrocytes and other mammalian cells. This toxin is encoded by the hlyA gene and is synthesized as a precursor form, prepro-HlyA. Prepro-HlyA consists of, from the amino terminus of this protein, a signal peptide, a pro-region, and a mature region. The pro-region is cleaved off extracellularly resulting in activation. To analyze the role of the pro-region, we substituted the native hlyA gene with the pro-region-deleted hlyA gene (hlyA delta pro). The hemolytic activity of the mutant organism was markedly decreased; the product of the hlyA delta pro gene, secreted in the periplasm, was degraded. To compare their abilities to form tertiary structure, the purified mature- and pro-HlyA were denatured and then renatured by reducing the concentration of denaturant; the denatured pro-HlyA recovered almost all activity while the mature-HlyA was not renatured. The sequences of the pro-region and a molecular chaperone, Hsp90, were similar. The pro-region expressed in Escherichia coli containing the hlyA delta pro gene increased the cytolytic activity. The purified pro-region peptide also facilitated renaturation of the denatured mature HlyA. These results suggest that the pro-region possibly guides the folding of the cytolysin similar to a molecular chaperone; the pro-region and molecular chaperones share common function and structure.