Analysis of CcpA mutations defective in carbon catabolite repression in Bacillus megaterium

Five mutations in ccpA of Bacillus megaterium with impaired functions were analysed for carbon catabolite repression. The phenotypes support the hypothesis that CcpA assumes a PurR/LacI fold. The completely inactive mutants CcpA119GE and CcpA326am cause alterations which are incompatible with that fold. A mutation with reduced activity, CcpA81GE, affects a site that would be partially surface exposed and may interfere with structure formation or cofactor binding. A mutation in the putative hinge alpha-helix, CcpA52AE, is negative transdominant over wild-type ccpA. The mutant CcpA38am is inactive, although reduced amounts of wild-type size protein are produced.