Two cAMP receptor proteins with different biochemical properties in the filamentous cyanobacterium Anabaena sp. PCC 7120

Two open reading frames (ORFs), alr0295 and alr2325, are found to encode putative cAMP receptor proteins (CRPs) in the genome of the filamentous cyanobacterium Anabaena sp. PCC 7120. These ORFs were named cAMP receptor protein-like gene A in Anabaena sp. PCC 7120 (ancrpA) and cAMP receptor protein-like gene B in Anabaena sp. PCC 7120 (ancrpB), respectively, and those translated products were investigated. The equilibrium dialysis measurements revealed that AnCrpA bound with cAMP specifically, while AnCrpB bound with both cAMP and cGMP, though the affinity for cGMP was weak. The binding affinity for cAMP of AnCrpA showed the lowest dissociation constant, approximately 0.8 microM, among bacterial CRPs. A gel mobility shift assay elucidated that AnCrpA and AnCrpB formed a complex with the consensus DNA sequence in the presence of cAMP, although AnCrpB did not have ordinary DNA-binding motifs.