Catalysis and structure of nitrogenases

In providing bioavailable nitrogen as building blocks for all classes of biomacromolecules, biological nitrogen fixation is an essential process for all organismic life. Only a single enzyme, nitrogenase, performs this task at ambient conditions and with ATP as an energy source. The assembly of the complex iron -sulfur enzyme nitrogenase and its catalytic mechanism re-mains a matter of intense study. Recent progress in the structural analysis of the three known isoforms of nitroge-nase-differentiated primarily by the heterometal in their active site cofactor-has revealed a degree of structural plasticity of these clusters that suggest two distinct binding sites for sub-strates and reaction intermediates. A mechanistic proposal based on this finding integrates most of the available experi-mental data. Furthermore, the first applications of high -resolution cryo-electron microscopy have highlighted further dynamic conformational changes. Structures obtained under turnover conditions support the proposed alternating half-site reactivity in the C2-symmetric nitrogenase complex.

Automated summary

Nitrogenase is an essential enzyme for all organismic life, providing bioavailable nitrogen for biomacromolecule synthesis. Recent studies have shown that nitrogenase has structural plasticity with multiple substrate binding sites, and dynamic conformational changes have been observed using cryo-electron microscopy. These findings contribute to a better understanding of the catalytic mechanism of nitrogenase.