FIGURE 1.

Alignment of the amino acid sequences of MerA ATII-LCL and the soil ortholog. The sequence of the soil enzyme is shown in bold and that of the ATII-LCL in light gray; the NmerA domain is underlined in black; the dimerization domain that is conserved among the homodimeric pyridine nucleotide-disulfide oxidoreductases is underlined in red; and the β-strand structures present in the dimerization domain are overlined in blue. The cysteine pairs 11/14 and 558/559 involved in binding of Hg²⁺, and cysteines 136/141, which form the disulfide bridge involved in Hg²⁺ reduction, are highlighted in yellow; negatively charged substitutions in MerA ATII-LCL are shown in red. The two sequences that contribute to thermostability are boxed in green (box1 and box2). The acidic residues marked M in the ATII-LCL sequence were replaced by the corresponding amino acids in the soil enzyme in the indicated ATII-LCL mutants.