Metal trafficking for nitrogen fixation: NifQ donates molybdenum to NifEN/NifH for the biosynthesis of the nitrogenase FeMo-cofactor
- Jose A. Hernandez*,†,
- Leonardo Curatti*,
- Constantino P. Aznar‡,
- Zinaida Perova*,
- R. David Britt‡, and
- Luis M. Rubio*,¶,§
- *Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; and
- ‡Department of Chemistry, University of California, Davis, CA 95616
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Edited by Bob B. Buchanan, University of California, Berkeley, CA, and approved June 3, 2008 (received for review April 14, 2008)
Abstract
The molybdenum nitrogenase, present in a diverse group of bacteria and archea, is the major contributor to biological nitrogen fixation. The nitrogenase active site contains an iron–molybdenum cofactor (FeMo-co) composed of 7Fe, 9S, 1Mo, one unidentified light atom, and homocitrate. The nifQ gene was known to be involved in the incorporation of molybdenum into nitrogenase. Here we show direct biochemical evidence for the role of NifQ in FeMo-co biosynthesis. As-isolated NifQ was found to carry a molybdenum–iron–sulfur cluster that serves as a specific molybdenum donor for FeMo-co biosynthesis. Purified NifQ supported in vitro FeMo-co synthesis in the absence of an additional molybdenum source. The mobilization of molybdenum from NifQ required the simultaneous participation of NifH and NifEN in the in vitro FeMo-co synthesis assay, suggesting that NifQ would be the physiological molybdenum donor to a hypothetical NifEN/NifH complex.
Footnotes
- ¶To whom correspondence should be addressed. E-mail: lrubio{at}nature.berkeley.edu
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Author contributions: J.A.H., L.C., R.D.B., and L.M.R. designed research; J.A.H., L.C., C.P.A., and Z.P. performed research; J.A.H., L.C., C.P.A., R.D.B., and L.M.R. analyzed data; and J.A.H., C.P.A., and L.M.R. wrote the paper.
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↵†Present address: Department of Biochemistry, Midwestern University, Glendale, AZ 85308.
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↵§Present address: Instituto Madrileño de Estudios Avanzados (IMDEA) Energia, Madrid 28023, Spain.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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See Commentary on page 11589.
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↵‖ In addition to its presence in the FeMo-cofactor of nitrogenase, biologically active molybdenum can be found constituting molybdopterin cofactors (Mo-co). Molybdoenzymes containing Mo-co are widely distributed in nature and participate in essential redox reactions of C, N, and S metabolisms (42).
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↵** NifB-co, the metabolic product of NifB activity, is an isolatable [Fe–S] cluster of unknown structure that serves as precursor to FeMo-co. NifB-co has also been proposed to be a precursor of the cofactors for the alternative nitrogenases, FeV-co and FeFe-co (43).
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This article contains supporting information online at www.pnas.org/cgi/content/full/0803576105/DCSupplemental.
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↵†† The VK-cluster is the [Fe–S] cluster precursor to FeMo-co that accumulates on NifEN in a ΔnifH mutant strain and is thought to represent an intermediate after NifB-co in FeMo-co synthesis (13).
- © 2008 by The National Academy of Sciences of the USA
