College of Letters & Science
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The College of Letters and Science, the largest center for learning, teaching and research at Montana State University, offers students an excellent liberal arts and sciences education in nearly 50 majors, 25 minors and over 25 graduate degrees within the four areas of the humanities, natural sciences, mathematics and social sciences.
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Item Proteomic Analysis of Methanococcus voltae Grown in the Presence of Mineral and Nonmineral Sources of Iron and Sulfur(American Society for Microbiology, 2022-08) Steward, Katherine F.; Payne, Devon; Kincannon, Will; Johnson, Christina; Lensing, Malachi; Fausset, Hunter; Németh, Brigitta; Shepard, Eric M.; Broderick, William E.; Broderick, Joan B.; Dubois, Jen; Bothner, BrianClusters of iron and sulfur are key components of the active sites of enzymes that facilitate microbial conversion of light or electrical energy into chemical bonds. The proteins responsible for transporting iron and sulfur into cells and assembling these elements into metal clusters are not well understood.Item Decarboxylation involving a ferryl, propionate, and a tyrosyl group in a radical relay yields heme b(2018-03) Streit, Bennett R.; Celis Luna, Arianna I.; Moraski, Garrett C.; Shisler, Krista A.; Shepard, Eric M.; Rodgers, Kenton R.; Lukat-Rodgers, Gudrun S.; DuBois, Jennifer L.The H2O2-dependent oxidative decarboxylation of coproheme III is the final step in the biosynthesis of heme b in many microbes. However, the coproheme decarboxylase reaction mechanism is unclear. The structure of the decarboxylase in complex with coproheme III suggested that the substrate iron, reactive propionates, and an active-site tyrosine convey a net 2e-/2H+ from each propionate to an activated form of H2O2 Time-resolved EPR spectroscopy revealed that Tyr-145 forms a radical species within 30 sec of the reaction of the enzyme-coproheme complex with H2O2 This radical disappeared over the next 270 sec, consistent with a catalytic intermediate. Use of the harderoheme III intermediate as substrate or substitutions of redox-active side chains (W198F, W157F, or Y113S) did not strongly affect the appearance or intensity of the radical spectrum measured 30 sec after initiating the reaction with H2O2, nor did it change the ~270 sec required for the radical signal to recede to ≤ 10% of its initial intensity. These results suggested Tyr-145 as the site of a catalytic radical involved in decarboxylating both propionates. Tyr-145 was accompanied by partial loss of the initially present Fe(III) EPR signal intensity, consistent with the possible formation of Fe(IV)=O. Site-specifically deuterated coproheme gave rise to a kinetic isotope effect of ~2 on the decarboxylation rate constant, indicating that cleavage of the propionate Cbeta-H bond was partly rate limiting. The inferred mechanism requires two consecutive hydrogen atom transfers, first from Tyr-145 to the substrate Fe/H2O2 intermediate and then from the propionate Cbeta-H to Tyr-145.Item Radical S -Adenosyl-l-methionine Chemistry in the Synthesis of Hydrogenase and Nitrogenase Metal Cofactors(2014-12) Byer, Amanda S.; Shepard, Eric M.; Peters, John W.; Broderick, Joan B.Nitrogenase, [FeFe]-hydrogenase, and [Fe]-hydrogenase enzymes perform catalysis at metal cofactors with biologically unusual non-protein ligands. The FeMo cofactor of nitrogenase has a MoFe7S9 cluster with a central carbon, whereas the H-cluster of [FeFe]-hydrogenase contains a 2Fe subcluster coordinated by cyanide and CO ligands as well as dithiomethylamine; the [Fe]-hydrogenase cofactor has CO and guanylylpyridinol ligands at a mononuclear iron site. Intriguingly, radical S-adenosyl-L-methionine enzymes are vital for the assembly of all three of these diverse cofactors. This minireview presents and discusses the current state of knowledge of the radical S-adenosylmethionine enzymes required for synthesis of these remarkable metal cofactors.