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Journal of Bacteriology, October 2007, p. 7475-7484, Vol. 189, No. 20
0021-9193/07/$08.00+0     doi:10.1128/JB.00891-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Archaeon Methanosarcina acetivorans Contains a Protein Disulfide Reductase with an Iron-Sulfur Cluster ^,

Department of Biochemistry and Molecular Biology and Penn State Astrobiology Research Center, 205 South Frear Laboratory, Pennsylvania State University, University Park, Pennsylvania 16802

Received 7 June 2007/ Accepted 24 July 2007

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 MA3736, 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 C₆₇ and C₇₀, while cysteines C₃₉ and C₁₀₇ 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.

Published ahead of print on 3 August 2007.

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