The School of Biological Sciences Spring 2025 MBM Seminar Series presents Dr. Rebbecah Warmack

Abstract: Biological nitrogen fixation, performed by the enzyme nitrogenase, supplies nearly 50% of the bioavailable nitrogen pool on Earth. However, the structural basis for its mechanism remains ambiguous. In particular, the structural intermediates involved in the enzyme’s catalytic cycle are unknown. My work is focused on the structural understanding of nitrogenase activity, isolated from A. vinelandii, and reacted under defined atmosphere environments using cryogenic electron microscopy (cryoEM). My application of anaerobic cryoEM to nitrogenase has facilitated views of its resting state as well as its state inactivated by reaction under alkaline conditions. This approach also facilitated high resolution structures of the nitrogenase MoFe-protein sampled along a time course of alkaline reaction mixtures under an acetylene atmosphere, revealing a sequence of salient active site changes. cryoEM also reveals unprecedented complexes, including that the nitrogenase associated factor T protein can recognize an alkaline inactivated MoFe-protein in vitro. The time-resolved studies illuminate structural rearrangements potentially relevant to nitrogen fixation by biological and synthetic clusters. My In situ studies of A. vinelandii reveal molecular assemblies associated with nitrogen fixation and offer a cellular context that could serve as a platform to investigate the structural and molecular events of nitrogen fixation.