title: XAFS studies of nitrogenase: the MoFe and VFe proteins and the use of crystallographic coordinates in three-dimensional EXAFS data analysis.
abstract: This paper reports a three-dimensional EXAFS refinement of the Mo coordination sphere of the FeMoco cluster of the dithionite-reduced MoFe protein from Klebsiella pneumoniae nitrogenase (Kp1) using the 1.6 A-resolution crystallographic coordinates. At this resolution, the positions of the heavy (Fe and S) atoms of the cluster are well determined and there is excellent agreement between the crystallographic and EXAFS models. However, the lighter homocitrate and histidine ligands are poorly determined in the crystal structure, and it is shown that the application of EXAFS-derived distance restraints during the early stages of crystallographic refinement provides a means of substantially improving (by approximately 0.1 A) the final crystallographic model. The consistency of the EXAFS analysis with the crystallographic information in this case justifies applications of EXAFS to cases where protein crystal structures are absent. Thus, the VFe protein of V-nitrogenase has been shown by EXAFS to possess a V-atom site catalytically similar to the well characterized MoFe-nitrogenases, with V replacing Mo.
authors.affiliation: Molecular Biophysics Group, CCLRC Daresbury Laboratory, Warrington, Cheshire WA4 4AD, UK. r.w.strange@dl.ac.uk
authors.forename: Richard W
authors.initials: RW
authors.lastname: Strange
authors.forename: Robert R
authors.initials: RR
authors.lastname: Eady
authors.forename: David
authors.initials: D
authors.lastname: Lawson
authors.forename: S Samar
authors.initials: SS
authors.lastname: Hasnain
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000595:Amino Acid Sequence; D016948:Azotobacter vinelandii / Q000201:enzymology; D018360:Crystallography, X-Ray / Q000379:methods; D008958:Models, Molecular; D009591:Nitrogenase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D009591:Nitrogenase