Open AccessXAFS studies of nitrogenase: the MoFe and VFe proteins and the use of crystallographic coordinates in three‐dimensional EXAFS data analysis
Author(s) -
Strange Richard W.,
Eady Robert R.,
Lawson David,
Hasnain S. Samar
Publication year - 2003
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049502017272
Subject(s) - extended x ray absorption fine structure , crystallography , crystal structure , chemistry , cluster (spacecraft) , multiple isomorphous replacement , x ray absorption fine structure , nitrogenase , dithionite , absorption spectroscopy , physics , spectroscopy , peptide sequence , organic chemistry , quantum mechanics , nitrogen fixation , computer science , nitrogen , programming language , biochemistry , enzyme , gene
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 Å‐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 ∼0.1 Å) 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.