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J. Biol. Chem., Vol. 283, Issue 37, 25178-25185, September 12, 2008

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A Novel Role for Human Nfs1 in the Cytoplasm

Nfs1 ACTS AS A SULFUR DONOR FOR MOCS3, A PROTEIN INVOLVED IN MOLYBDENUM COFACTOR BIOSYNTHESIS^*

Zvonimir Marelja, Walter Stöcklein, Manfred Nimtz, and Silke Leimkühler¹

From the Institute of Biochemistry and Biology, University of Potsdam, D-14476 Potsdam, Germany and the Helmholtz Center for Infection Research, 38124 Braunschweig, Germany

The human MOCS3 gene encodes a protein involved in activation and sulfuration of the C terminus of MOCS2A, the smaller subunit of the molybdopterin (MPT) synthase. MPT synthase catalyzes the formation of the dithiolene group of MPT that is required for the coordination of the molybdenum atom in the last step of molybdenum cofactor (Moco) biosynthesis. The two-domain protein MOCS3 catalyzes both the adenylation and the subsequent generation of a thiocarboxylate group at the C terminus of MOCS2A by its C-terminal rhodanese-like domain (RLD). The low activity of MOCS3-RLD with thiosulfate as sulfur donor and detailed mutagenesis studies showed that thiosulfate is most likely not the physiological sulfur source for Moco biosynthesis in eukaryotes. It was suggested that an L-cysteine desulfurase might be involved in the sulfuration of MOCS3 in vivo. In this report, we investigated the involvement of the human L-cysteine desulfurase Nfs1 in sulfur transfer to MOCS3-RLD. A variant of Nfs1 was purified in conjunction with Isd11 in a heterologous expression system in Escherichia coli, and the kinetic parameters of the purified protein were determined. By studying direct protein-protein interactions, we were able to show that Nfs1 interacted specifically with MOCS3-RLD and that sulfur is transferred from L-cysteine to MOCS3-RLD via an Nfs1-bound persulfide intermediate. Because MOCS3 was shown to be located in the cytosol, our results suggest that cytosolic Nfs1 has an important role in sulfur transfer for the biosynthesis of Moco.

Received for publication, May 28, 2008 , and in revised form, July 21, 2008.

^* This work was supported in part by Deutsche Forschungsgemeinschaft Grant LE1171/5-3 and the Fonds der Chemischen Industrie. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. S1.

¹ To whom correspondence should be addressed. Tel.: 49-331-977-5603; Fax: 49-331-977-5419; E-mail: sleim{at}uni-potsdam.de.

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