Sulfite binding pocket of MjFsrI-C and ANME2c-FsrII-6D-C. Structural alignments of A. fulgidus DsrA with MjFsrI-C and ANME2c-FsrII-6D-C, respectively. The protein backbones of A. fulgidus DsrA, MjFsrI-C, and ANME2c-FsrII-6D-C are in deep salmon, orange, and yellow, respectively. Carbon atoms of residues involved in the formation of sulfite binding site of A. fulgidus DsrA and MjFsrI-C/ANME2c-FsrII-6D-C are in red and purple, respectively. The residue numbers correspond to A. fulgidus DsrA (red) and MjFsrI-C/ANME2c-FsrII-6D-C (purple). For siroheme and sulfite the following color code is used: green, carbon; blue, nitrogen; red, oxygen; yellow, sulfur; orange, iron.