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J. Biol. Chem., Vol. 281, Issue 48, 36701-36709, December 1, 2006

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Purification of a NifEN Protein Complex That Contains Bound Molybdenum and a FeMo-Co Precursor from an Azotobacter vinelandii nifHDK Strain^*

From the Department of Plant and Microbial Biology, University of California at Berkeley, Berkeley, California 94720

The NifEN protein complex serves as a molecular scaffold where some of the steps for the assembly of the iron-molybdenum cofactor (FeMo-co) of nitrogenase take place. A His-tagged version of the NifEN complex has been previously purified and shown to carry two identical [4Fe-4S] clusters of unknown function and a [Fe-S]-containing FeMo-co precursor. We have improved the purification of the his-NifEN protein from a nifHDK strain of Azotobacter vinelandii and have found that the amounts of iron and molybdenum within NifEN were significantly higher than those reported previously. In an in vitro FeMo-co synthesis system with purified components, the NifEN protein served as a source of both molybdenum and a [Fe-S]-containing FeMo-co precursor, showing significant FeMo-co synthesis activity in the absence of externally added molybdate. Thus, the NifEN scaffold protein, purified from nifHDK background, contained the Nif-Bco-derived Fe-S cluster and molybdenum, although these FeMo-co constituents were present at different levels within the protein complex.

Received for publication, July 18, 2006 , and in revised form, August 31, 2006.

^* This work was supported by NIGMS, National Institutes of Health Grant 35332. 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.

¹ To whom correspondence should be addressed: Dept. of Plant and Microbial Biology, University of California-Berkeley, 111 Koshland Hall, Berkeley, CA 94720-3102. Tel.: 510-643-3940; Fax: 510-642-4995; E-mail: lrubio{at}nature.berkeley.edu.

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				L. Curatti, J. A. Hernandez, R. Y. Igarashi, B. Soboh, D. Zhao, and L. M. Rubio In vitro synthesis of the iron molybdenum cofactor of nitrogenase from iron, sulfur, molybdenum, and homocitrate using purified proteins PNAS, November 6, 2007; 104(45): 17626 - 17631. [Abstract] [Full Text] [PDF]