Nitrogenase MoFe-Protein at 1.16 Å Resolution: A Central Ligand in the FeMo-Cofactor
A high-resolution crystallographic analysis of the nitrogenase MoFe-protein reveals a previously unrecognized ligand coordinated to six iron atoms in the center of the catalytically essential FeMo-cofactor. The electron density for this ligand is masked in structures with resolutions lower than 1.55 angstroms, owing to Fourier series termination ripples from the surrounding iron and sulfur atoms in the cofactor. The central atom completes an approximate tetrahedral coordination for the six iron atoms, instead of the trigonal coordination proposed on the basis of lower resolution structures. The crystallographic refinement at 1.16 angstrom resolution is consistent with this newly detected component being a light element, most plausibly nitrogen. The presence of a nitrogen atom in the cofactor would have important implications for the mechanism of dinitrogen reduction by nitrogenase.
Additional Information© 2002 American Association for the Advancement of Science. 13 May 2002; Accepted 26 June 2002. This work was supported by NIH. Stanford Synchrotron Radiation Laboratory operations are funded by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, and NIH. F.A.T. acknowledges the Burroughs Wellcome Fund and the Helen Hay Whitney Foundation for postdoctoral fellowships. We thank J. C. Peters, J. E. Bercaw, and H. B. Gray for enlightening discussions. Coordinates of the refined MoFe-protein structure have been deposited in the Protein Data Bank (accession code 1M1N).
Supplemental Material - Einsle1073877.sup.pdf