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Journal of Bacteriology, June 2007, p. 4391-4400, Vol. 189, No. 12
0021-9193/07/$08.00+0     doi:10.1128/JB.00166-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Enzymology and Evolution of the Pyruvate Pathway to 2-Oxobutyrate in Methanocaldococcus jannaschii{triangledown}

Randy M. Drevland,1 Abdul Waheed,1,{dagger} and David E. Graham1,2*

Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712,1 Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 787122

Received 1 February 2007/ Accepted 6 April 2007

The archaeon Methanocaldococcus jannaschii uses three different 2-oxoacid elongation pathways, which extend the chain length of precursors in leucine, isoleucine, and coenzyme B biosyntheses. In each of these pathways an aconitase-type hydrolyase catalyzes an hydroxyacid isomerization reaction. The genome sequence of M. jannaschii encodes two homologs of each large and small subunit that forms the hydrolyase, but the genes are not cotranscribed. The genes are more similar to each other than to previously characterized isopropylmalate isomerase or homoaconitase enzyme genes. To identify the functions of these homologs, the four combinations of subunits were heterologously expressed in Escherichia coli, purified, and reconstituted to generate the iron-sulfur center of the holoenzyme. Only the combination of MJ0499 and MJ1277 proteins catalyzed isopropylmalate and citramalate isomerization reactions. This pair also catalyzed hydration half-reactions using citraconate and maleate. Another broad-specificity enzyme, isopropylmalate dehydrogenase (MJ0720), catalyzed the oxidative decarboxylation of ß-isopropylmalate, ß-methylmalate, and D-malate. Combined with these results, phylogenetic analysis suggests that the pyruvate pathway to 2-oxobutyrate (an alternative to threonine dehydratase in isoleucine biosynthesis) evolved several times in bacteria and archaea. The enzymes in the isopropylmalate pathway of leucine biosynthesis facilitated the evolution of 2-oxobutyrate biosynthesis through the introduction of a citramalate synthase, either by gene recruitment or gene duplication and functional divergence.

* Corresponding author. Mailing address: Department of Chemistry and Biochemistry, University of Texas at Austin, 1 University Station A5300, Austin, TX 78712. Phone: (512) 471-4491. Fax: (512) 471-8696. E-mail: degraham{at}mail.utexas.edu

{triangledown} Published ahead of print on 20 April 2007.

{dagger} Present address: Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.

Journal of Bacteriology, June 2007, p. 4391-4400, Vol. 189, No. 12
0021-9193/07/$08.00+0     doi:10.1128/JB.00166-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Boyd, J. M., Drevland, R. M., Downs, D. M., Graham, D. E. (2009). Archaeal ApbC/Nbp35 Homologs Function as Iron-Sulfur Cluster Carrier Proteins. J. Bacteriol. 191: 1490-1497 [Abstract] [Full Text]  
  • Drevland, R. M., Jia, Y., Palmer, D. R. J., Graham, D. E. (2008). Methanogen Homoaconitase Catalyzes Both Hydrolyase Reactions in Coenzyme B Biosynthesis. J. Biol. Chem. 283: 28888-28896 [Abstract] [Full Text]  
  • Namboori, S. C., Graham, D. E. (2008). Acetamido Sugar Biosynthesis in the Euryarchaea. J. Bacteriol. 190: 2987-2996 [Abstract] [Full Text]  


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