The archaeon Methanosarcina acetivorans contains a protein disulfide reductase with an iron-sulfur cluster

Methanosarcina acetivorans, a strictly anaerobic methane-producing species belonging to the domain Archaea, contains a gene cluster annotated with homologs encoding oxidative stress proteins. One of the genes (MA3736) is annotated as a gene encoding an uncharacterized carboxymuconolactone decarboxylase, an enzyme required for aerobic growth with aromatic compounds by species in the domain Bacteria. Methane producing species are not known to utilize aromatic compounds, suggesting that MA3736 is incorrectly annotated. The product of NW736, overproduced in Escherichia coli, had protein disulfide reductase activity dependent on a C67XXC70 motif not found in carboxymuconolactone decarboxylase. We propose that MA3736 be renamed mdrA (methanosarcina disulfide reductase). Further, unlike carboxymuconolactone decarboxylase, MdrA contained an Fe-S cluster. Binding of the Fe-S cluster was dependent on essential cysteines C-67 and C-70, while cysteines C-39 and C-107 were not required. Loss of the Fe-S cluster resulted in conversion of MdrA from an inactive hexamer to a trimer with protein disulfide reductase activity. The data suggest that MdrA is the prototype of a previously unrecognized protein disulfide reductase family which contains an intermolecular Fe-S cluster that controls oligomerization as a mechanism to regulate protein disulfide reductase activity.