NifH: Structural and Mechanistic Similarities with Proteins Involved in Diverse Biological Processes

The NifH protein is a subunit of the nitrogenase enzyme that catalyzes the reduction of atmospheric nitrogen to ammonia. This protein contains highly conserved regions including the nucleotide binding sites, metal center ligands and the Switch I and Switch II domains. A number of proteins have structural and mechanistic similarities as well as evolutionary relationships with the NifH protein, notable among them being: light independent protochlorophyllide (Pchlide) reductase (ChlL/FrxC or bChL), arsenite pump ATPase (ArsA), 2-hydroxyglutaryl dehydratase Component A (CompA) involved in glutamate degradation and MinD that functions in spatial regulation of cell division. Although involved in very diverse biological processes, these proteins share an underlying common structural framework. This review mainly focuses on the structural similarities of these proteins with the NifH protein and discusses recent reports of complementation studies involving NifH and few of the proteins mentioned.