Carbonic anhydrase from Methanosarcina thermophila: proposal of a new class of carbonic anhydrases and putative roles for the enzyme in anaerobic acetate catabolism

Carbonic anhydrase (CA) from acetate-grown Methanosarcina thermophila strain TM-1 was purified> 10,OOO-fold (22% recovery) to apparent homogeneity and a specific activity of 4,900 units mg⁻¹.The gene encoding this CA was isolated fronl a partial genomic library on a 12-kb fragment and sequenced. Comparison of the deduced anlino acid sequence with the N-terminaI sequence of the purified protein shows that the gene encodes an additional 34 N-terminal residues with properties characteristic of signal peptides in secretory proteins. The deduced amino acid sequence has no significant identity to any known CAs, but has, among others, 35% sequence identity to the first 197 deduced N-terminal amino acids of a proposed CO₂-concentrating-mechanism protein from Synechococcus sp. strain PCC7942.