Molecular symmetry of the MoFe protein of nitrogenase. Structural homology/nitrogen fixation/x-ray crystallography.

X-ray diffraction data to 2.4-A resolution have been collected for native monoclinic crystals of the MoFe protein of nitrogenase from Clostridium pasteurianum. The MoFe protein is an alpha 2 beta 2 tetramer of 220,000 molecular weight with 1 molecule in the crystallographic asymmetric unit. A 6-A resolution rotation function shows the orientation of the crystallographic diad and pseudo mutually perpendicular diads representing 2-fold relationships between alpha and beta chains. Hence, at least at low resolution, there exists structural homology between these two polypeptide chains.