Structural homologies between the amino acid sequence of Clostridium pasteurianum MoFe protein and the DNA sequences of nifD and K genes of phylogenetically diverse bacteria

Abstract

The complete amino acid sequence of the larger (α-) subunit and about 70% of the total sequence of the smaller (β-) subunit of the MoFe protein from Clostridium pasteurianum was determined by analyses of peptides derived from BrCN cleavage and by digestions with trypsin, staphylococcal protease and lysylendo-peptidase of the separated subunits. The α-subunit has 529 amino acid residues, giving an M _r value of 58 774. This is the first complete sequence for the α-subunit of an isolated MoFe protein. In comparing the sequences of both subunits to those from other sources, 5 out of 9 cysteines in the α-subunit and 3 out of 6 in the β-subunit are invariant, thus suggesting a function as ligands to FeS and MoFeS clusters in the MoFe protein. All of these cysteines are located in the amino terminal halves of both subunits.