Evolution of a new enzyme for carbon disulphide conversion by an acidothermophilic archaeon

Many extremophilic organisms require unusual enzymes to help them survive in harsh environments. For example, acid-loving hyperthermophilic Archaea found in the bubbling mud of volcanic solfataras are able to oxidize reduced sulphur compounds. The X-ray crystal structure of a carbon disulphide (CS2) hydrolase from an Acidianus strain isolated from the Solfatara volcano near Naples, Italy, has now been determined. The enzyme, which converts CS2 into hydrogen sulphide and carbon dioxide, has a typical carbonic anhydrase fold and active site, although CO2 is not a substrate for the enzyme. This suggests that CS2 hydrolase is an example of divergent evolution, where a new enzyme has emerged through the evolution of a new quaternary structure rather than through mutations of the active site.