Structure and catalytic mechanism of the β-carbonic anhydrases

The β-carbonic anhydrases (β-CAs) are a diverse but structurally related group of zinc-metalloenzymes found in eubacteria, plant chloroplasts, red and green algae, and in the Archaea. The enzyme catalyzes the rapid interconversion of CO2 and H2O to HCO3− and H+, and is believed to be associated with metabolic enzymes that consume or produce CO2 or HCO3−. For many organisms, β-CA is essential for growth at atmospheric concentrations of CO2. Of the five evolutionarily distinct classes of carbonic anhydrase, β-CA is the only one known to exhibit allosterism. Here we review the structure and catalytic mechanism of β-CA, including the structural basis for allosteric regulation.