ADP-ribosylation, a mechanism regulating nitrogenase activity

Nitrogen fixation is the vital biochemical process in which atmospheric molecular nitrogen is made available to the biosphere. The process is highly energetically costly and thus tightly regulated. The activity of the key enzyme, nitrogenase, is controlled by reversible mono-ADP-ribosylation of one of its components, the Fe protein. This protein provides the other component, the MoFe protein, with the electrons required for the reduction of molecular nitrogen. The Fe-protein is ADP-ribosylated and de-ADP-ribosylated by dinitrogenase reductase ADP-ribosyl transferase and dinitrogenase reductase activating glycohydrolase, respectively. Here we review the current biochemical and structural knowledge of this central regulatory reaction.