Iron-sulfur (Fe:S) centers in proteins exhibit a diverse range of structures and functional properties. X-ray diffraction methods will be used to determine the three-dimensional structures of three Fe:S proteins involved in electron transfer reactions: the nitrogenase molybdenum-iron protein from Azotobacter vinelandii and the rubredoxin and ferredoxin from the hyperthermophile Pyrococcus furiosis. The crystallographic structures will permit an evaluation of the roles of the polypeptide and iron-sulfur centers in controlling the redox properties and electron transfer mechanisms of these proteins. The specific structural objectives of this proposal are: Nitrogenase molybdenum-iron protein. The molybdenum iron (MoFe-) protein component of nitrogenase contains the site of substrate reduction, an iron-sulfur-molybdenum cofactor of presently unknown structure. The functional roles of the clusters and protein will be addressed by crystallographic studies to at least 2.5A resolution of the A. vinelandii MoFe-protein in the presence and absence of bound ligands (inhibitor and nucleotides) and in different oxidation states: mutant MoFe-proteins; and structures of alternative nitrogenase proteins related to MoFe-protein. Thermostable rubredoxin and ferredoxin. The archaebacterium Pyrococcus furiosis is a hyperthermophile that grows at 1000C. Crystallographic structures of the rubredoxin (refined to at least 0.96A resolution) and ferredoxin from this organism will not only define the details of the protein-Fe:S center interactions, but will also provide a structural framework for characterizing the thermostability of these proteins.
