Bacterial ι-carbonic anhydrase: a new active class of carbonic anhydrase identified in the genome of the Gram-negative bacterium Burkholderia territorii.

The carbonic anhydrases (CAs, EC 4.2.1.1) catalyse a simple but physiologically crucial reversible reaction, the carbon dioxide hydration with the production of bicarbonate and protons. In the last years, and especially, to the rapid emergence of the bacterial antibiotic resistance that is occurring worldwide, the understanding of the function of bacterial CAs has increased significantly. Recently, a new CA-class (ι-CA) was discovered in the marine diatom T. pseudonana. It has been reported that bacterial genomes may contain genes with relevant homology to the diatom ι-class CA. Still, the catalytic activity of the enzyme encoded by the gene was not investigated. Thus, herein, for the first time, we cloned, expressed, and purified the recombinant bacterial ι-CA (acronym BteCAι) identified in the genome of Burkholderia territorii. The recombinant BteCAι resulted in a good catalyst for the hydration of CO2 to bicarbonate and protons, with a kcat of 3.0 × 105 s -1 and kcat/KM of 3.9 × 107 M -1 s -1, and is also sensitive to inhibition by the sulphonamide acetazolamide. Furthermore, with the aid of the protonography, it has been demonstrated that BteCAι can be present as a dimer. This result is corroborated by the construction of a molecular model of BteCAι, which showed that the enzyme is formed by two equivalent monomers having a structure similar to a butterfly.