Analysis of acidic surface of Haloferax mediterranei glucose dehydrogenase by site-directed mutagenesis

Generally, halophilic enzymes present a characteristic amino acid composition, showing an increase in the content of acidic residues and a decrease in the content of basic residues, particularly lysines. The latter decrease appears to be responsible for a reduction in the proportion of solvent-exposed hydrophobic surface. This role was investigated by site-directed mutagenesis of glucose dehydrogenase from Haloferax mediterranei, in which surface aspartic residues were changed to lysine residues. From the biochemical analysis of the mutant proteins, it is concluded that the replacement of the aspartic residues by lysines results in slightly less halotolerant proteins, although they retain the same enzymatic activities and kinetic parameters compared to the wild type enzyme.