Biochemical properties of a new alpha-carbonic anhydrase from the human pathogenic bacterium, Vibrio cholerae

Vibrio cholerae, a Gram-negative bacterium, is the causative agent of cholera and colonizes the upper small intestine where sodium bicarbonate is present at a high concentration. Sodium bicarbonate is a potential inducer of virulence gene expression. Bacteria can increase cytosolic bicarbonate levels through the existence of transporter family proteins or through the action of metalloenzymes, called carbonic anhydrases (CAs, EC 4.2.1.1). Vibrio cholerae, lacking of transporter proteins in its genome, utilizes the CA system to accumulate bicarbonate into the cell suggesting a pivotal role of this metalloenzymes in the microbial virulence. Here, we report for the first time the characterization of the alpha-CA of V. cholerae (VchCA), which has been identified by translated genome inspection. The alpha-CA encoding gene was cloned and expressed in Escherichia coli and the recombinant protein purified to homogeneity. This investigation aimed to study the biochemical properties of VchCA and to provide preliminary insights in the field of this pathogen virulence. VchCA has a low esterase activity with 4-nitrophenyl acetate as substrate, and a high activity for the hydration of CO2 to bicarbonate.