Evolution of carbonic anhydrases in fungi

The ubiquitous metalloenzyme carbonic anhydrase (CA) catalyzes the interconversion of carbon dioxide and bicarbonate. This enzyme has been investigated in mammals, plants, algae, bacteria, archaea and fungi. Based on distinct structural characteristics, CAs can be assigned to five independently evolved classes (alpha, beta, gamma, delta and zeta). beta-CAs can be further subdivided into plant-type and cab-type sub-classes. The recent characterization of CAs in fungi led us to initiate a systematic search for these enzymes in filamentous ascomycetes. The genomes of basidiomycetes and hemiascomycetous yeasts contain only beta-CAs, while the filamentous ascomycetes also possess genes encoding alpha-class CAs. Here, we present a phylogenetic analysis of 97 fungal CA sequences that addresses the diversification of fungal CAs. During evolution various gene duplication and gene loss events seem to be the cause for the multiplicity of CAs in filamentous ascomycetes. Our data revealed that during the evolution of filamentous ascomycetes, a gene encoding the plant-type beta-CA was duplicated, resulting in two closely related isoforms, one with and one without an N-terminal mitochondrial target sequence (MTS). The acquisition of the MTS most likely took place after the gene duplication event and after the evolutionary separation of the fungal orders Sordariales and Eurotiales.