Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
10 results
Search Results
Item Pathways of Iron and Sulfur Acquisition, Cofactor Assembly, Destination, and Storage in Diverse Archaeal Methanogens and Alkanotrophs(2021-08) Johnson, Christina; England, Alexis; Munro-Ehrlich, Mason; Colman, Daniel R.; DuBois, Jennifer L.; Boyd, Eric S.Archaeal methanogens, methanotrophs, and alkanotrophs have a high demand for iron (Fe) and sulfur (S); however, little is known of how they acquire, traffic, deploy, and store these elements. Here, we examined the distribution of homologs of proteins mediating key steps in Fe/S metabolism in model microorganisms, including iron(II) sensing/uptake (FeoAB), sulfide extraction from cysteine (SufS), and the biosynthesis of iron-sulfur [Fe-S] clusters (SufBCDE), siroheme (Pch2 dehydrogenase), protoheme (AhbABCD), cytochrome c (Cyt c) (CcmCF), and iron storage/detoxification (Bfr, FtrA, and IssA), among 326 publicly available, complete or metagenome-assembled genomes of archaeal methanogens/methanotrophs/alkanotrophs. The results indicate several prevalent but nonuniversal features, including FeoB, SufBC, and the biosynthetic apparatus for the basic tetrapyrrole scaffold, as well as its siroheme (and F430) derivatives. However, several early-diverging genomes lacked SufS and pathways to synthesize and deploy heme. Genomes encoding complete versus incomplete heme biosynthetic pathways exhibited equivalent prevalences of [Fe-S] cluster binding proteins, suggesting an expansion of catalytic capabilities rather than substitution of heme for [Fe-S] in the former group. Several strains with heme binding proteins lacked heme biosynthesis capabilities, while other strains with siroheme biosynthesis capability lacked homologs of known siroheme binding proteins, indicating heme auxotrophy and unknown siroheme biochemistry, respectively. While ferritin proteins involved in ferric oxide storage were widespread, those involved in storing Fe as thioferrate were unevenly distributed. Collectively, the results suggest that differences in the mechanisms of Fe and S acquisition, deployment, and storage have accompanied the diversification of methanogens/methanotrophs/alkanotrophs, possibly in response to differential availability of these elements as these organisms evolved.Item H/D exchange mass spectrometry and statistical coupling analysis reveal a role for allostery in a ferredoxin-dependent bifurcating transhydrogenase catalytic cycle(2018-01) Berry, Luke; Poudel, Saroj; Tokmina-Lukaszewska, Monika; Colman, Daniel R.; Nguyen, Diep M. N.; Schut, Gerrit J.; Adams, Michael W. W.; Peters, John W.; Boyd, Eric S.; Bothner, BrianRecent investigations into ferredoxin-dependent transhydrogenases, a class of enzymes responsible for electron transport, have highlighted the biological importance of flavin-based electron bifurcation (FBEB). FBEB generates biomolecules with very low reduction potential by coupling the oxidation of an electron donor with intermediate potential to the reduction of high and low potential molecules. Bifurcating systems can generate biomolecules with very low reduction potentials, such as reduced ferredoxin (Fd), from species such as NADPH. Metabolic systems that use bifurcation are more efficient and confer a competitive advantage for the organisms that harbor them. Structural models are now available for two NADH-dependent ferredoxin-NADP(+) oxidoreductase (Nfn) complexes. These models, together with spectroscopic studies, have provided considerable insight into the catalytic process of FBEB. However, much about the mechanism and regulation of these multi-subunit proteins remains unclear. Using hydrogen/deuterium exchange mass spectrometry (HDX-MS) and statistical coupling analysis (SCA), we identified specific pathways of communication within the model FBEB system, Nfn from Pyrococus furiosus, under conditions at each step of the catalytic cycle. HDX-MS revealed evidence for allosteric coupling across protein subunits upon nucleotide and ferredoxin binding. SCA uncovered a network of co-evolving residues that can provide connectivity across the complex. Together, the HDX-MS and SCA data show that protein allostery occurs across the ensemble of iron-sulfur cofactors and ligand binding sites using specific pathways that connect domains allowing them to function as dynamically coordinated units.Item Defining Electron Bifurcation in the Electron Transferring Flavoprotein Family(2017-11) Garcia Costas, Amaya M.; Poudel, Saroj; Miller, Anne-Frances; Schut, Gerrit J.; Ledbetter, Rhesa N.; Fixen, Kathryn R.; Seefeldt, Lance C.; Adams, Michael W. W.; Harwood, Caroline S.; Boyd, Eric S.; Peters, John W.Electron bifurcation is the coupling of exergonic and endergonic redox reactions to simultaneously generate (or utilize) low and high potential electrons. It is the third recognized form of energy conservation in biology and has recently been described in select electron transferring flavoproteins (Etfs). Etfs are flavin-containing heterodimers best known for donating electrons derived from fatty acid and amino acid oxidation to an electron transfer respiratory chain via ETF quinone oxidoreductase. Canonical examples contain a flavin adenine dinucleotide (FAD) that is involved in electron transfer as well as a non-redox active adenosine monophosphate (AMP). However, Etfs demonstrated to bifurcate electrons contain a second FAD in place of the AMP. To expand our understanding of the functional variety and metabolic significance of Etfs and to identify amino acid sequence motifs that potentially enable electron bifurcation, we compiled 1,314 Etf protein sequences from genome sequence databases and subjected them to informatics and structural analyses. Etfs were identified in diverse archaea and bacteria, and these clustered into five distinct well-supported groups based on amino acid sequences. Gene neighborhood analyses indicate that these Etf group designations largely correspond to putative differences in functionality. Etfs with the demonstrated ability to bifurcate were found to form one group, suggesting distinct and conserved amino acid sequence motifs enable this capability. Indeed, structural modeling and sequence alignments revealed that identifying residues occur in the NADH and FAD-binding regions of bifurcating Etfs. Collectively, a new classification scheme is presented for Etf proteins that demarcates putative bifurcating vs. non-bifurcating members and suggests that Etf mediated bifurcation is associated with surprisingly diverse enzymes.IMPORTANCE Electron bifurcation has recently been recognized as an electron transfer mechanism used by microorganisms to maximize energy conservation. Bifurcating enzymes couple thermodynamically unfavorable reactions with thermodynamically favorable reactions in an overall spontaneous process. Here we show that the electron transferring flavoprotein (Etf) enzyme family exhibits far greater diversity than previously recognized and we provide a phylogenetic analysis that clearly delineates bifurcating and non-bifurcating members of this family. Structural modeling of proteins within these groups reveals key differences between the bifurcating and non-bifurcating Etfs.Item Two functionally distinct NADP(+)-dependent ferredoxin oxidoreductases maintain the primary redox balance of Pyrococcus furiosus(2017-07) Nguyen, Diep M. N.; Schut, Gerrit J.; Zadvornyy, Oleg A.; Tokmina-Lukaszewska, Monika; Poudel, Saroj; Lipscomb, Gina L.; Adams, Leslie A.; Dinsmore, Jessica T.; Nixon, William J.; Boyd, Eric S.; Bothner, Brian; Peters, John W.; Adams, Michael W. W.Electron bifurcation has recently gained acceptance as the third mechanism of energy conservation in which energy is conserved through the coupling of exergonic and endergonic reactions. A structure-based mechanism of bifurcation has been elucidated recently for the flavin-based enzyme NADH-dependent ferredoxin NADP+ oxidoreductase I (NfnI) from the hyperthermophillic archaeon Pyrococcus furiosus. NfnI is thought to be involved in maintaining the cellular redox balance, producing NADPH for biosynthesis by recycling the two other primary redox carriers, NADH and ferredoxin. The P. furiosus genome encodes an NfnI paralog termed NfnII, and the two are differentially expressed depending on the growth conditions. In this study, we show that deletion of the genes encoding either NfnI or NfnII affects the cellular concentrations of NAD(P)H and particularly NADPH. This results in a moderate to severe growth phenotype in deletion mutants, demonstrating a key role for each enzyme in maintaining redox homeostasis. Despite their similarity in primary sequence and cofactor content, crystallographic, kinetic, and mass spectrometry analyses reveal that there are fundamental structural differences between the two enzymes and NfnII does not catalyze the NfnI bifurcating reaction. Instead it exhibits non-bifurcating ferredoxin NADP oxidoreductase-type activity. NfnII is therefore proposed to be a bifunctional enzyme and to also catalyze a bifurcating reaction, although its third substrate, in addition to ferredoxin and NADP(H), is as yet unknown.Item Identification and characterization of a novel member of the radical AdoMet enzyme superfamily and implications for the biosynthesis of the Hmd hydrogenase active site cofactor(2009-11) McGlynn, Shawn E.; Boyd, Eric S.; Shepard, Eric M.; Lange, Rachel K.; Gerlach, Robin; Broderick, Joan B.; Peters, John W.The genetic context, phylogeny, and biochemistry of a gene flanking the H2-forming methylene-H4-methanopterin dehydrogenase gene (hmdA), here designated hmdB, indicate that it is a new member of the radical S-adenosylmethionine enzyme superfamily. In contrast to the characteristic CX3CX2C or CX2CX4C motif defining this family, HmdB contains a unique CX5CX2C motif.Item Diversity, abundance, and potential activity of nitrifying and nitrate-reducing microbial assemblages in a subglacial ecosystem(2011-05) Boyd, Eric S.; Lange, Rachel K.; Mitchell, Andrew C.; Havig, Jeff R.; Lafreniere, M. J.; Shock, Everett L.; Peters, John W.; Skidmore, Mark L.Subglacial sediments sampled from beneath Robertson Glacier (RG), Alberta, Canada, were shown to harbor diverse assemblages of potential nitrifiers, nitrate reducers, and diazotrophs, as assessed by amoA, narG, and nifH gene biomarker diversity. Although archaeal amoA genes were detected, they were less abundant and less diverse than bacterial amoA, suggesting that bacteria are the predominant nitrifiers in RG sediments. Maximum nitrification and nitrate reduction rates in microcosms incubated at 4°C were 280 and 18.5 nmol of N per g of dry weight sediment per day, respectively, indicating the potential for these processes to occur in situ. Geochemical analyses of subglacial sediment pore waters and bulk subglacial meltwaters revealed low concentrations of inorganic and organic nitrogen compounds. These data, when coupled with a C/N atomic ratio of dissolved organic matter in subglacial pore waters of ∼210, indicate that the sediment communities are N limited. This may reflect the combined biological activities of organic N mineralization, nitrification, and nitrate reduction. Despite evidence of N limitation and the detection of nifH, we were unable to detect biological nitrogen fixation activity in subglacial sediments. Collectively, the results presented here suggest a role for nitrification and nitrate reduction in sustaining microbial life in subglacial environments. Considering that ice currently covers 11% of the terrestrial landmass and has covered significantly greater portions of Earth at times in the past, the demonstration of nitrification and nitrate reduction in subglacial environments furthers our understanding of the potential for these environments to contribute to global biogeochemical cycles on glacial-interglacial timescales.Item Hydrogenase activity of mineral-associated and suspended populations of Desulfovibrio desulfuricans Essex 6(2014-02) Reardon, Catherine L.; Magnuson, Timothy S.; Boyd, Eric S.; Leavitt, W. D.; Reed, D. W.; Geesey, Gill G.The interactions between sulfate-reducing microorganisms and iron oxides influence a number of important redox-sensitive biogeochemical processes including the formation of iron sulfides. Enzymes, such as hydrogenase which catalyze the reversible oxidation of molecular hydrogen, are known to mediate electron transfer to metals and may contribute to the formation and speciation of ferrous sulfides formed at the cell–mineral interface. In the present study, we compared the whole cell hydrogenase activity of Desulfovibrio desulfuricans strain Essex 6 growing as biofilms on hematite (hematite-associated) or as suspended populations using different metabolic pathways. Hematite-associated cells exhibited significantly greater hydrogenase activity than suspended populations during sulfate respiration but not during pyruvate fermentation. The enhanced activity of the hematite-associated, sulfate-grown cells appears to be dependent on iron availability rather than a general response to surface attachment since the activity of glass-associated cells did not differ from that of suspended populations. Hydrogenase activity of pyruvate-fermenting cells was stimulated by addition of iron as soluble Fe(II)Cl2 and, in the absence of added iron, both sulfate-reducing and pyruvate-fermenting cells displayed similar rates of hydrogenase activity. These data suggest that iron exerts a stronger influence on whole cell hydrogenase activity than either metabolic pathway or mode of growth. The location of hydrogenase to the cell envelope and the enhanced activity at the hematite surface in sulfate-reducing cells may influence the redox conditions that control the species of iron sulfides on the mineral surface.Item Unification of [FeFe]-hydrogenases into Three Structural and Functional Groups(2016-09) Poudel, Saroj; Tokmina-Lukaszewska, Monika; Colman, Daniel R.; Refai, Mohammed Y.; Schut, Gerrit J.; King, Paul W.; Maness, Pin-Ching; Adams, Michael W. W.; Peters, John W.; Bothner, Brian; Boyd, Eric S.Background: [FeFe]-hydrogenases (Hyd) are structurally diverse enzymes that catalyze the reversible oxidation of hydrogen (H2). Recent biochemical data demonstrate new functional roles for these enzymes, including those that function in electron bifurcation where an exergonic reaction is coupled with an endergonic reaction to drive the reversible oxidation/production of H2. Methods: To identify the structural determinants that underpin differences in enzyme functionality, a total of 714 homologous sequences of the catalytic subunit, HydA, were compiled. Bioinformatics approaches informed by biochemical data were then used to characterize differences in inferred quaternary structure, HydA active site protein environment, accessory iron-sulfur clusters in HydA, and regulatory proteins encoded in HydA gene neighborhoods. Results: HydA homologs were clustered into one of three classification groups, Group 1 (G1), Group 2 (G2), and Group 3 (G3). G1 enzymes were predicted to be monomeric while those in G2 and G3 were predicted to be multimeric and include HydB, HydC (G2/G3) and HydD (G3) subunits. Variation in the HydA active site and accessory iron-sulfur clusters did not vary by group type. Group-specific regulatory genes were identified in the gene neighborhoods of both G2 and G3 Hyd. Analyses of purified G2 and G3 enzymes by mass spectrometry strongly suggest that they are post-translationally modified by phosphorylation. Conclusions: These results suggest that bifurcation capability is dictated primarily by the presence of both HydB and HydC in Hyd complexes, rather than by variation in HydA. General significance: This classification scheme provides a framework for future biochemical and mutagenesis studies to elucidate the functional role of Hyd enzymes.Item Aerobic and Anaerobic Thiosulfate Oxidation by a Cold-Adapted, Subglacial Chemoautotroph(2015-12) Harrold, Zoe R.; Skidmore, Mark L.; Hamilton, Trinity L.; Desch, Elizabeth; Kirina, Amada; van Gelder, Will; Glover, Kevin; Roden, Eric E.; Boyd, Eric S.Geochemical data indicate that protons released during pyrite (FeS2) oxidation are important drivers of mineral weathering in oxic and anoxic zones of many aquatic environments including those beneath glaciers. Oxidation of FeS2 under oxic, circumneutral conditions proceeds through the metastable intermediate thiosulfate (S2O32-), which represents an electron donor capable of supporting microbial metabolism. Subglacial meltwaters sampled from Robertson Glacier (RG), Canada over a seasonal melt cycle reveal concentrations of S2O32- that are typically below detection despite the presence of available pyrite and several orders of magnitude higher concentrations of the FeS2 oxidation product sulfate (SO42-). Here we report the physiological and genomic characterization of the chemolithoautotrophic facultative anaerobe Thiobacillus sp. RG5 isolated from the subglacial environment at RG. The RG5 genome encodes pathways for the complete oxidation of S2O32-, CO2 fixation, and aerobic and anaerobic respiration with nitrite or nitrate. Growth experiments indicate that the energy required to synthesize a cell under oxygen or nitrate reducing conditions with S2O32- as electron donor was lower at 5.1 °C than 14.4 °C, indicating that this organism is cold-adapted. RG sediment-associated soxB transcripts, which encode a component of the S2O32--oxidizing complex, were closely affiliated to soxB from RG5. Collectively, these results suggest an active sulfur cycle in the subglacial environment at RG mediated in part by populations closely affiliated with RG5. Microbial consumption of S2O32- by RG5-like populations may accelerate abiotic FeS2 oxidation thereby enhancing mineral weathering in the subglacial environment.Item [FeFe]-Hydrogenase Abundance and Diversity along a Vertical Redox Gradient in Great Salt Lake, USA(2014-12) Boyd, Eric S.; Hamilton, Trinity L.; Swanson, Kevin D.; Howells, Alta E.; Meuser, Jonathan E.; Posewitz, Matthew C.; Peters, John W.The use of [FeFe]-hydrogenase enzymes for the biotechnological production of H2 or other reduced products has been limited by their sensitivity to oxygen (O2). Here, we apply a PCR-directed approach to determine the distribution, abundance, and diversity of hydA gene fragments along co-varying salinity and O2 gradients in a vertical water column of Great Salt Lake (GSL), UT. The distribution of hydA was constrained to water column transects that had high salt and relatively low O2 concentrations. Recovered HydA deduced amino acid sequences were enriched in hydrophilic amino acids relative to HydA from less saline environments. In addition, they harbored interesting variations in the amino acid environment of the complex H-cluster metalloenzyme active site and putative gas transfer channels that may be important for both H2 transfer and O2 susceptibility. A phylogenetic framework was created to infer the accessory cluster composition and quaternary structure of recovered HydA protein sequences based on phylogenetic relationships and the gene contexts of known complete HydA sequences. Numerous recovered HydA are predicted to harbor multiple N- and C-terminal accessory iron-sulfur cluster binding domains and are likely to exist as multisubunit complexes. This study indicates an important role for [FeFe]-hydrogenases in the functioning of the GSL ecosystem and provides new target genes and variants for use in identifying O2 tolerant enzymes for biotechnological applications.