TcpP protein is a positive regulator of virulence gene expression in Vibrio cholerae

The production of several virulence factors in Vibrio cholerae O1, including cholera toxin and the pilus colonization factor TCP (toxin-coregulated pilus), is strongly influenced by environmental conditions. To specifically identify membrane proteins involved in these signal transduction events, we examined a transposon library of V. cholerae generated by Tn bla mutagenesis for cells that produce TCP when grown under various nonpermissive conditions. To select for TCP-producing cells we used the recently described bacteriophage CTXΦ-Kan, which uses TCP as its receptor and carries a gene encoding resistance to kanamycin. Among the isolated mutants was a transposon insertion in a gene homologous to nqrB from Vibrio alginolyticus , which encodes a subunit of a Na + -translocating NADH:ubiquinone oxidoreductase, and tcpI , encoding a chemoreceptor previously implicated in the negative regulation of TCP production. A third transposon mutant had an insertion in tcpP , which is in an operon with tcpH , a known positive regulator of TCP production. However, TcpP was shown to be essential for TCP production in V. cholerae , as a tcpP -deletion strain was deficient in pili production. The amino-terminal region of TcpP shows sequence homology to the DNA-binding domains of several regulatory proteins, including ToxR from V. cholerae and PsaE from Yersinia pestis . Like ToxR, TcpP activates transcription of the toxT gene, an essential activator of tcp operon transcription. Furthermore, TcpH, with its large periplasmic domain and inner membrane anchor, has a structure similar to that of ToxS and was shown to enhance the activity of TcpP. We propose that TcpP/TcpH constitute a pair of regulatory proteins functionally similar to ToxR/ToxS and PsaE/PsaF that are required for toxT transcription in V. cholerae .