Sequestration of carbon dioxide by the hydrophobic pocket of the carbonic anhydrases

The interaction between carbon dioxide (CO2) and the alpha-class carbonic anhydrase, human CA 2 (HCA2) exists for only a short period due to the rapid catalytic turnover by this enzyme. The fleeting nature of this interaction has led to difficulties in its direct analysis, with previous studies placing the CO2 in the hydrophobic pocket of HCA2's active site. A more precise location was determined via the crystal structure of CO2 trapped in both wild-type (holo) and zinc-free (apo) HCA2. This provided a detailed description of the means by which CO2 is held and orientated for optimal catalysis. This information can be extended to the beta and gamma class enzymes to help elucidate the binding mode of CO2 in these enzymes. (C) 2009 Elsevier B.V. All rights reserved.