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Journal of Bacteriology, October 2007, p. 7392-7398, Vol. 189, No. 20
0021-9193/07/$08.00+0     doi:10.1128/JB.00876-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Expression and Association of Group IV Nitrogenase NifD and NifH Homologs in the Non-Nitrogen-Fixing Archaeon Methanocaldococcus jannaschii ^,

Christopher R. Staples,¹ Surobhi Lahiri,² Jason Raymond,³ Lindsay Von Herbulis,^4,5 Biswarup Mukhophadhyay,^4,5,6 and Robert E. Blankenship^2*

Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287-1604,¹ Departments of Biology and Chemistry, Washington University, Saint Louis, Missouri 63130,² Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550,³ Virginia Bioinformatics Institute,⁴ Departments of Biochemistry,⁵ Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061⁶

Received 5 June 2007/ Accepted 19 July 2007

Using genomic analysis, researchers previously identified genes coding for proteins homologous to the structural proteins of nitrogenase (J. Raymond, J. L. Siefert, C. R. Staples, and R. E. Blankenship, Mol. Biol. Evol. 21:541-554, 2004). The expression and association of NifD and NifH nitrogenase homologs (named NflD and NflH for "Nif-like" D and H, respectively) have been detected in a non-nitrogen-fixing hyperthermophilic methanogen, Methanocaldococcus jannaschii. These homologs are expressed constitutively and do not appear to be directly involved with nitrogen metabolism or detoxification of compounds such as cyanide or azide. The NflH and NflD proteins were found to interact with each other, as determined by bacterial two-hybrid studies. Upon immunoisolation, NflD and NflH copurified, along with three other proteins whose functions are as yet uncharacterized. The apparent presence of genes coding for NflH and NflD in all known methanogens, their constitutive expression, and their high sequence similarity to the NifH and NifD proteins or the BchL and BchN/BchB proteins suggest that NflH and NflD participate in an indispensable and fundamental function(s) in methanogens.

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* Corresponding author. Mailing address: Departments of Biology and Chemistry, Campus Box 1137, Washington University, Saint Louis, MO 63130. Phone: (314) 935-7971. Fax: (314) 935-4432. E-mail: Blankenship{at}wustl.edu

Published ahead of print on 27 July 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

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Journal of Bacteriology, October 2007, p. 7392-7398, Vol. 189, No. 20
0021-9193/07/$08.00+0     doi:10.1128/JB.00876-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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