A Bigger Picture: USU Biochemists Advance Knowledge of Life-Critical Enzyme

Utah State University researchers and collaborators are solving a long-standing mystery of how bacterial enzymes known as nitrogenases convert nitrogen into life-sustaining compounds on which all plants and animals depend. Their discoveries could have energy-saving implications for the world’s food supply.

A paper describing the findings by USU biochemists Lance Seefeldt and Zhiyong Yang, Dmitriy Lukoyanov and Brian M. Hoffman of Northwestern University, Virginia Tech’s Dennis Dean and Brett Barney of the University of Minnesota, appears in the March 26, 2012, online early edition of the Proceedings of the National Academy of Sciences. The team’s research is supported by the National Institutes of Health and the National Science Foundation.

“The structure of nitrogenases and the general site at which nitrogen gets bound and reduced has been known for more than 15 years,” says Seefeldt, professor in USU’s Department of Chemistry and Biochemistry and recipient of the university’s 2012 D. Wynne Thorne Career Research Award. “During the past seven years, we’ve identified several steps in this process. Now, for the first time, we’ve started to establish the bigger picture: the mechanistic pathway by which this process takes place.”

Nitrogen, in the form of dinitrogen, he says, makes up about 80 percent of the air we breathe. Though essential for all life on the planet, it’s not in a form higher organisms can directly access. Humans and animals take in nitrogen — in the form of protein — from food; plants obtain nitrogen from the soil.

“It’s an incredible irony,” Seefeldt says. “We need nitrogen to survive and we’re swimming in a sea of it, yet we can’t get to it.”

The process by which nitrogen is converted to ammonia, a form organisms can use, is complex, Seefeldt says.

“Nitrogen bonds are very strong and difficult to break,” he says. “Two known processes break the bonds and allow conversion. One is a natural, bacterial process. The other is the man-made Häber-Bosch process. The world’s food supply currently depends equally on each of these.”

The century-old Häber-Bosch process, used to make agricultural fertilizers, is energy-intensive and depends heavily on fossil fuels, Seefeldt says, so interest is high in harnessing and making more use of the cleaner, natural process.

“By finally unlocking the conversion process, we can look to Mother Nature for answers,” he says.

To identify the process, the research team has developed and refined a chemical methodology to trap and detect intermediates in nitrogen-catalyzed reductions and flash-freeze samples.

Barney, a former postdoctoral fellow at USU and now an assistant professor at U of M, likens the effort to capturing single frames of a movie on a moving film reel.

“You have to capture each step of the process in the act and freeze the frame, so you can actually examine it and understand what it does,” he says.

Yang, a doctoral candidate in Seefeldt’s lab, says the team now has the whole “reel;” they just need to define each frame of the “movie.”

“Soon, we’ll be able to see the entire picture,” he says. “We’ll be able to describe each step, at the mechanistic level, of one of the most vital processes to life on Earth.”

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