Site-directed mutagenesis of lysine 58 in a putative ATP-binding domain of the calmodulin-sensitive adenylate cyclase from Bordetella pertussis abolishes catalytic activity

Abstract

A 2.7-kb cya A gene fragment encoding the amino-terminal end of the calmodulin-sensitive adenylate cyclase from Bordetella pertussis has been placed under the control of the lac promoter for expression in Escherichia coli. Following induction with isopropyl beta-D-thiogalactoside, calmodulin-sensitive adenylate cyclase activity was detected in a cell extract from E. coli. The expression vector directed the synthesis of a 90-kDa polypeptide that was recognized by rabbit polyclonal antibodies raised against the catalytic subunit of B. pertussis adenylate cyclase. Inspection of the deduced amino acid sequence of the cya A gene product revealed a sequence with homology to consensus sequences for an ATP-binding domain found in many ATP-binding proteins. On the basis of the analysis of nucleotide binding proteins, a conserved lysine residue has been implicated in the binding of ATP. A putative ATP-binding domain in the B. pertussis adenylate cyclase possesses an analogous lysine residue at position 58. To test whether lysine 58 of the B. pertussis adenylate cyclase is a crucial residue for enzyme activity, it was replaced with methionine by oligonucleotide-directed mutagenesis. E. coli cells were transformed with the mutant cya A gene, and the expressed gene product was characterized. The mutant protein exhibited neither basal nor calmodulin-stimulated enzyme activity, indicating that lysine 58 plays a critical role in enzyme catalysis.