Belt-sulfur mobilization as a crucial mechanistic feature shared between the vanadium and molybdenum nitrogenases

Nitrogenase catalyzes the reduction of N₂ to NH₃ at its active site cofactor. Recent studies of the “conventional” Mo-nitrogenase suggest a plausible involvement of all cofactor belt-S sites in catalysis. Here, we use analytical, enzymatic, and spectroscopic methods to demonstrate the same dynamic belt-S mobilization by the “alternative” V-nitrogenase during catalysis. Our results point to belt-S turnover as a common catalytic feature of the homologous Mo- and V-nitrogenases while identifying an activated but N₂-free conformation of the V-nitrogenase that holds great potential for facilitating future mechanistic explorations of the intriguing nitrogenase enzyme.