The protein sequence of an archaeal catalase-peroxidase

The gene encoding a catalase-peroxidase of archaeal origin, the halophilic catalase-peroxidase from Haloarcula marismortui, was sequenced. The primary structure proposed was confirmed by Edman degradation and mass spectrometry analyses of proteolytic fragments of the purified protein. The open reading frame in the gene corresponds to 731 amino acids and the calculated mass of the mature protein (deleted of the N-terminal methionine) is 81,253.65 Da, in reasonable agreement with the value of 81,292 +/- 9 Da previously measured by mass spectrometry. Southern and Northern blot analyses showed that the protein is encoded by a single gene as a monocistronic transcript. The protein sequence shows a high level of identity with bacterial catalase-peroxidases, with strongly conserved regions around the heme binding histidines. Similarly to other soluble halophilic proteins, it shows the excess of acidic residues that has been associated with solvation in halophilic adaptation.