Biochemistry and Functional Genomics of Methanococcus Jannaschii

Virginia Polytechnic Institute And State University, Blacksburg VA

Investigators

Abstract

The methanogenic archaea convert simple carbon compounds into methane gas. Because biologically produced methane is both a commercially attractive energy source and a greenhouse gas, it is desirable to find methods to regulate methanogenesis. This project uses comparative genomics, analytical biochemistry, enzyme purification, protein chemistry and molecular genetics to identify new genes that are required for growth and methane formation in the complete genome sequence of one of the best-studied methanogens, Methanococcus jannaschii. This autolithotrophic organism uses hydrogen to reduce carbon dioxide to methane and produces all the organic compounds that it requires for growth from gases and minerals released from mid-ocean hydrothermal vent fluids. To catalyze these reactions, M. jannaschii requires at least 19 organic coenzymes including seven coenzymes that are essential for methane formation. This project will identify and characterize enzymes from M. jannaschii that are required for the biosynthesis of coenzymes and amino acids, but have not yet been identified from that organism's complete genome sequence. These "invisible" enzymes are attractive targets for designing specific inhibitors of methanogenesis. Two coenzymes produced by M. jannaschii, riboflavin and the deaza-riboflavin coenzyme F420, are derived from a common precursor. Although both archaea and eukaryotes biosynthesize this precursor by the same pathway, the archaea use different enzymes to catalyze several reactions including the GTP cyclohydrolase and pyrimidine deaminase steps. In addition to studying these unique enzymes, this project will characterize proteins involved in subsequent steps of coenzyme F420 biosynthesis, including the CofC, CofD,CofE, CofG and CofH proteins. This research also studies novel enzymes required for the biosynthesis of 4-aminobenzoic acid (used to produce the methanopterin coenzyme). Finally, this project will identify "invisible" enzymes that catalyze proline, cysteine and methionine amino acid biosyntheses, 3-dehydroquinate biosynthesis (a precursor of aromatic amino acids) and purine nucleotide biosynthesis. The microorganism Methanococcus jannaschii grows in mid-ocean hydro thermal vents, using hydrogen and carbon dioxide to make methane gas. This project uses molecular genetic, biochemical and computational techniques to identify new genes in the complete genome sequence of M. jannaschii that are required for growth and methane formation. Results from this research will help explain how methanogenic organisms have evolved to produce methane and suggest molecular targets for the beneficial regulation of biological methane formation, useful to produce fuel or to reduce greenhouse gas emissions.