The Sixteenth Iron in the Nitrogenase MoFe Protein

摘要

The nitrogenase molybdenum-iron (MoFe) protein contains two types of metalloclusters, the [8Fe:7S] P-cluster and the [7Fe:9S:Mo:C:homocitrate] FeMo cofactor, which have been the focus of considerable interest to define their roles in the mechanism of biological nitrogen fixation. Along with these two metalloclusters, a third metal binding site is present in the MoFe protein that has attracted much less attention. The metal at this site has been assigned to either Ca~(2+) or Mg~(2+) in different MoFe protein structures and is positioned at the interface between the two P-subunits: approximately 25 A and 21 A away from the P-cluster and FeMo-cofactor, respectively.