White, an associate professor of biochemistry at Virginia Tech, is interested in how metabolic systems evolved. He will report significant advancements in understanding of Archaea at the 222nd national meeting of the American Chemical Society Aug. 26-30 in Chicago.
White is working with Methanococcus jannaschi, which was the first Archaea bacteria to have its genome sequenced (Reported in Science on Aug. 23,1996, by Carol Bult and 38 others). It has 1,800 genes -- the smallest genome of organisms in the Archaea domain.
Archaea live in environments ranging from volcanic vents on the sea floor to salt ponds. Methanococcus jannaschi lives on carbon dioxide (CO2) in about 90 degrees C (194 F) at 2,500 meters of ocean depth (8,000 feet). It reduces CO2 to hydrogen -- its source of energy for its life processes -- and exhales methane. White is determining which of the 1,800 genes are responsible for the individual steps in the biosynthesis of the coenzymes carrying out this process. He is in the process of identifying the 200 genes that dictate the formation of the 20 coenzymes in Methanococcus jannaschi. Coenzymes are the molecules that bind with proteins to create enzymes, the catalysts of metabolic processes.
"Now we can compare Methanococcus jannaschii's genes with the genetic sequences of other life forms," White points. "Many of the genes produce proteins that we would expect to be involved in metabolic processes. But there are many metabolic steps in this organism that are completely different from that found in the Eukarya or Bacterial domains. Archaea have these foreign genes that don't fit into contemporary biochemistry. Is it because they are hot bacteria -- they evolved differently in response to living close to the boiling point of water? Or is there some other explanation? It's a real mystery."
Many of the enzymes White has discovered have never before been identified. He has also discovered previously unrecognized metabolic reactions of some well-known coenzymes.
During his presentation, he will discuss compounds involved in the chemistry of metabolizing CO2, particularly coenzyme M, methanofuran, methanopterin, coenzyme F420, and coenzyme B. In the coenzyme M biosynthetic pathway, for example, White's research team has characterized the first enzyme catalyzing the addition of bisulfite to phosphoenolpyruvate, a new route for the formation of carbon-sulfur bonds. They have also discovered new enzymes that hydrolyze mono-phosphate esters. F420 is the coenzyme that causes methanogenic bacteria to fluoresce blue-green. White has shown that F420 formation uses four previously unknown enzymes, one of which uses a reaction like that found in DNA polymerase, thus establishing a link between the genes and the coenzymes.
"We can extrapolate from this information how the earliest forms of life functioned -- such as the reactions used to synthesize genes. It's the same chemistry that creates RNA and DNA in other forms of life," says White.
White's talk, "Biosynthesis of methanogenic cofactors (BIOL 156)," is scheduled for Wednesday, Aug. 29, from 4:30 to 4:55 p.m., at the McCormick Place North, Room N231, Level 2.
The Surprising Archaea: Discovering another domain of life, by John L. Howland (Oxford University Press, 2000) is an interesting book about Archaea, including their role in camels' digestive systems.
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