By Hardin Young
Nitrogen is essential for life. It's needed to build proteins, DNA and many other components of cells. Although nitrogen gas makes up almost 80% of Earth's atmosphere, most organisms cannot use it directly. Certain microbes solve this problem through a process called nitrogen fixation, which converts nitrogen gas into ammonia. This process is carried out by an enzyme called nitrogenase.
Understanding how this enzyme functions could have major implications for more efficient, biologically based production of ammonia, a crucial component of common fertilizers.
A molecular off switch for nitrogen fixation
A collaborative research team from across the U.S., brought together by a research group at the University of Arkansas, studied nitrogenase and its regulation in a methane-producing microbe known as a methanogen. Using high-resolution cryo-electron microscopy, they discovered that methanogen nitrogenase can bind with regulatory proteins to form a large inactive complex—what the authors call a protein supercomplex.
The newly identified supercomplex functions as a molecular off switch, preventing nitrogen fixation when energy or nutrients are limited. Signals that reflect the cell's energy and nutrient levels can break apart this complex and restore enzyme activity, allowing nitrogen fixation to resume.
"This discovery reveals an entirely new strategy for regulating one of the most important biochemical reactions on Earth," said Dan Lessner, professor of biological sciences at the University of Arkansas and corresponding author of the study published in Nature.
The finding is important because nitrogen fixation supports agriculture, food production and ecosystems around the world. It also advances understanding of microbial physiology, the global nitrogen cycle and the evolution of nitrogen fixation while providing insights that could inform future biotechnology and sustainable agriculture applications.
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