title: Fe protein-independent substrate reduction by nitrogenase MoFe protein variants.
abstract: The reduction of substrates catalyzed by nitrogenase normally requires nucleotide-dependent Fe protein delivery of electrons to the MoFe protein, which contains the active site FeMo cofactor. Here, it is reported that independent substitution of three amino acids (β-98(Tyr→His), α-64(Tyr→His), and β-99(Phe→His)) located between the P cluster and FeMo cofactor within the MoFe protein endows it with the ability to reduce protons to H2, azide to ammonia, and hydrazine to ammonia without the need for Fe protein or ATP. Instead, electrons can be provided by the low-potential reductant polyaminocarboxylate-ligated Eu(II) (Em values of -1.1 to -0.84 V vs the normal hydrogen electrode). The crystal structure of the β-98(Tyr→His) variant MoFe protein was determined, revealing only small changes near the amino acid substitution that affect the solvent structure and the immediate vicinity between the P cluster and the FeMo cofactor, with no global conformational changes observed. Computational normal-mode analysis of the nitrogenase complex reveals coupling in the motions of the Fe protein and the region of the MoFe protein with these three amino acids, which suggests a possible mechanism for how Fe protein might communicate subtle changes deep within the MoFe protein that profoundly affect intramolecular electron transfer and substrate reduction.
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Karamatullah
authors.initials: K
authors.lastname: Danyal
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Rasmussen
authors.affiliation: ∥Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Keable
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Boyd S
authors.initials: BS
authors.lastname: Inglet
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Sudipta
authors.initials: S
authors.lastname: Shaw
authors.affiliation: ∥Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Zadvornyy
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Simon
authors.initials: S
authors.lastname: Duval
authors.affiliation: ‡Department of Biochemistry, Virginia Tech University, Blacksburg, Virginia 24061, United States.
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Dean
authors.affiliation: §Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, Washington 99352, United States.
authors.forename: Simone
authors.initials: S
authors.lastname: Raugei
authors.affiliation: ∥Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
authors.forename: John W
authors.initials: JW
authors.lastname: Peters
authors.affiliation: †Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
authors.forename: Lance C
authors.initials: LC
authors.lastname: Seefeldt
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D019943:Amino Acid Substitution; D016948:Azotobacter vinelandii / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D003067:Coenzymes / Q000737:chemistry* / Q000235:genetics; D003198:Computer Simulation; D007501:Iron / Q000737:chemistry*; D008982:Molybdenum / Q000737:chemistry*; D020125:Mutation, Missense; D009591:Nitrogenase / Q000737:chemistry* / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D003067:Coenzymes; D008982:Molybdenum; D000255:Adenosine Triphosphate; D007501:Iron; D009591:Nitrogenase