Unravelling Catalytic Divergence in Mo- and Fe-Only Nitrogenases: The Role of the Heterometal-Site and Protein Environment from QM/MM Insights
Justin P. Joyce, Ragnar Bjornsson, Serena DeBeer
TL;DR
This paper investigates how molybdenum and iron-only nitrogenases differ in their catalytic behavior using quantum mechanical and molecular mechanical models.
Contribution
The study reveals structural and electronic differences in the metal sites of Mo- and Fe-only nitrogenases that explain their distinct reactivity.
Findings
FeFeco exhibits two low-lying E1 states due to sulfide protonation.
FeMoco strictly favors μ2-sulfide protonation in its E1 state.
FeFeco's unique μ3-sulfide-protonated state may explain its divergent reactivity.
Abstract
Two key characteristics differentiate molybdenum-dependent (MoFe) and iron-only (FeFe) nitrogenases: their efficacy for N2 fixation and their product distributions for CO2 reduction, yielding HCO2 – and CH4, respectively. Despite their divergent properties, prior research argues that the distinct cofactors share a common mechanism and equivalent structures with the addition of “n” electrons and protons at their E n catalytic states. The proposed equivalence between the cofactors was foundational in the assignment of an Fe-hydride at their E1 states based on interpretation of FeFeco’s photolabile and thermolabile E1 isomers (Inorg. Chem. 2022, 61, 5459–5464). However, the E0 state crystal structures of FeMoco and FeFeco have sharp, previously unaddressed distinctions in their metal–metal distances and proximal residue identities at their respective octahedral M-sites (M = Mo or Fe).…
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Taxonomy
TopicsMetalloenzymes and iron-sulfur proteins · Ammonia Synthesis and Nitrogen Reduction · Organometallic Complex Synthesis and Catalysis