Reconstructing the Evolutionary History of Nitrogenases: Evidence for Ancestral Molybdenum-Cofactor Utilization

Abstract

15The nitrogenase metalloenzyme family, essential for supplying fixed nitrogen to the biosphere, is 16 one of life's key biogeochemical innovations. The three isozymes of nitrogenase differ in their 17 metal dependence, each binding either a FeMo-, FeV-, or FeFe-cofactor for the reduction of 18 nitrogen. The history of nitrogenase metal dependence has been of particular interest due to the 19 possible implication that ancient marine metal availabilities have significantly constrained 20 nitrogenase evolution over geologic time. Here, we combine phylogenetics and ancestral sequence 21 reconstruction -a method by which inferred, historical protein sequence information can be 22 linked to functional molecular properties -to reconstruct the metal dependence of ancient 23 nitrogenases. Inferred ancestral nitrogenase sequences at the deepest nodes of the phylogeny 24