The molybdoenzyme dimethylsulfoxide (DMSO) reductase contributes to the release
of dimethylsulfide, a compound that has been implicated in cloud nucleation and
global climate regulation. The crystal structure of DMSO reductase from
Rhodobacter sphaeroides reveals a monooxo molybdenum cofactor containing two
molybdopterin guanine dinucleotides that asymmetrically coordinate the
molybdenum through their dithiolene groups. One of the pterins exhibits
different coordination modes to the molybdenum between the oxidized and reduced
states, whereas the side chain oxygen of Ser147 coordinates the metal in both
states. The change in pterin coordination between the Mo(VI) and Mo(IV) forms
suggests a mechanism for substrate binding and reduction by this enzyme.
Sequence comparisons of DMSO reductase with a family of bacterial
oxotransferases containing molybdopterin guanine dinucleotide indicate a similar
polypeptide fold and active site with two molybdopterins within this family.
