Newswise — Scientists know a lot about plant photosynthesis, which reduces carbon dioxide in the atmosphere. They know far less about how microbes that live in soil and elsewhere keep methane, the second most important greenhouse gas, from entering the atmosphere.
In the Sept. 10 issue of the journal Science, researchers from the University of Kansas and Iowa State University describe the structure of an unusual molecule that is key to how those microbes work.
David Graham, associate professor of civil, architectural and environmental engineering, says that the molecule is remarkable for more than its crucial role in helping bacterial enzymes break down methane. The molecule also has antibiotic properties and even potential use as a water-cleaning agent for the semiconductor industry.
Graham got his first hint of the molecule's existence as a graduate student 15 years ago. Five years later, he and Alan DiSpirito, associate professor of microbiology from Iowa State University, were at a meeting when they started talking about the source of an odd yellow color each was seeing in water surrounding the different bacteria they were studying. The molecule was identical to a molecule that James Zahn, a graduate student under DiSpirito, had purified in association with the enzyme responsible for methane oxidation.
They guessed that the bacteria might be producing a special molecule that, acting outside the bacteria, caused the yellowness. Proving the molecule existed would take years, and detailing its structure even longer.
By 1998, Graham and DiSpirito had grasped about 70 percent of the molecule's structure. They were stuck until Hyung Kim, a student of Graham's who is now a postdoctoral fellow at the University of Minnesota, figured out a better way to purify the molecule; then the researchers could bring all its parts into view.
"After 10 years of preliminary work, Kim tried a scientific trick, and after a final test that lasted 36 hours, they had the structure," Graham said.
Two factors had made it difficult to determine the molecule's structure. First, it was novel. There was nothing like it in existing databases. Second, the molecule's presumed job was to bring copper inside the bacteria, and copper fouls up many instruments that help scientists determine a molecule's structure.
The bacteria needed extra copper because they feast on methane, and methane is very stable, Graham said. A potent metal is needed to crack the molecule, and copper, which is highly reactive, is nature's main tool for doing that. The newly discovered molecule latches fiercely to copper. Then it brings the copper inside the cell, where it seems to team up with a key enzyme that actually breaks down the methane.
In the course of trying to get the molecule's structure, DiSpirito's group discovered it had antibiotic and antioxidant properties, Graham said. "That's important," he added, "because we're continuously looking for antibiotics."
For another, its unique and aggressive binding of copper might serve semiconductor makers, who need water that is copper-free. The natural molecule might become a blueprint for synthesizing one the industry can use.
The finding also is important, Graham said, for those who develop models of climate change and global warming. The rate at which methane escapes the Earth's surface in any given period of time varies from hundreds to thousands of times at different locations, he said. Knowing the structure of the molecule should allow researchers to understand why.
Until now, Graham said, scientists haven't known the details of what goes on at a molecular level when methane is broken down. Now that they do, it's possible to refine calculations surrounding the release of methane into the atmosphere. That, in turn, should eventually improve the accuracy and predictive power of climate-change models.
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