Cyclic AMP-dependent functional forms of cyclic AMP receptor protein from Vibrio cholerae

The cyclic AMP receptor protein (CRP) from Escherichia coli, involved in the transcriptional regulation of a number of genes and operons, works by binding to specific sites upstream of promoters. CRP also binds cyclic AMP (cAMP), and this binding, which causes conformational changes in CRP, is mandatory for its activity. A cAMP-dependent variation in the conformation as well as biological activity of E. coli CRP has been reported, with the cAMP–CRP complex formed at high cAMP concentrations resembling the uncomplexed apoprotein CRP. CRP from Vibrio cholerae, which plays an important role in the regulation of virulence gene expression, has a 95% sequence identity with the E. coli protein. We have purified and characterized V. cholerae CRP and studied its transcription activation properties as a function of increasing cAMP concentrations. A biphasic dependence on cAMP levels was observed, similar to that found for E.coli CRP. The implications of these results on regulation of cAMP–CRP dependent promoters in V. cholerae has been discussed.