Nitrogenase MoFe-Protein at 1.16 Å Resolution: A Central Ligand in the FeMo-Cofactor

• Published in: Science (American Association for the Advancement of Science) 2002-09, Vol.297 (5587), p.1696-1700
• Main Authors: Einsle, Oliver, Tezcan, F. Akif, Susana L. A. Andrade, Schmid, Benedikt, Yoshida, Mika, Howard, James B., Rees, Douglas C.
• Format: Article
• Language: English
• Subjects: Ammonia; Atoms; Atoms & subatomic particles; Azotobacter vinelandii - enzymology; Biochemistry; Biological and medical sciences; Cell metabolism, cell oxidation; Cell physiology; Coenzymes - chemistry; Coenzymes - metabolism; Crystallography; Crystallography, X-Ray; Electron density; Electronic structure; Electrons; Fundamental and applied biological sciences. Psychology; Iron; Ligands; Metalloproteins; Models, Molecular; Molecular and cellular biology; Molybdoferredoxin - chemistry; Molybdoferredoxin - metabolism; Nitrogen; Nitrogen - chemistry; Nitrogenase; Nitrogenase - chemistry; Nitrogenase - metabolism; Oxygen; Protein Conformation; Proteins; Sulfur
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1073877

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.