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2011 Annual Science Report

Montana State University Reporting  |  SEP 2010 – AUG 2011

Executive Summary

Iron-sulfur clusters are ubiquitous in biology and possess features that are reminiscent of the features of iron-sulfur minerals. The structure/reactivity relationships between iron-sulfur metalloenzymes and iron-sulfur minerals has been noted by a number of investigators and is the basis for aspects of a “Metabolism First” origin of life scenario and more specifically for the “Iron Sulfur World”. These relationships provide a framework for the research being conducted at the Astrobiology Biogeocatalysis Research Center (ABRC) with a focus on revealing the connection between iron-sulfur minerals and iron-sulfur metalloenzymes. The adaptation of iron-sulfur motifs from the abiotic world to the biological world may have been an early event in the generation of the building blocks of life on Earth and possibly a common feature of life elsewhere in the universe. ABRC research is aimed at providing the structural and chemical determinants that define the catalytic properties ... Continue reading.

Field Sites
9 Institutions
12 Project Reports
34 Publications
5 Field Sites

Project Reports

  • Minerals to Enzymes: The Path to CO Dehydrogenase/Acetyl – CoA Synthase

    We have through NAI Director’s discretionary initiated a project to probing the structural determinants for nickel-iron-sulfur based reversible carbon monoxide oxidation. We are probing whether we can mimic the reactivity of carbon monoxide dehydrogenase to some extent by simple organic nesting and synthesis of nickel-iron-sulfur clusters using a model system we have developed.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2
  • Paradigms for Complex Iron-Sulfur Cluster Assembly and the Origin and Evolution of Iron-Sulfur Enzymes

    We have presented seminal results in the past year that define paradigms for iron-sulfur cluster assembly in biology that are shared between several important enzymes systems. This work has allowed for the formulation of new models for the origin and evolution of iron sulfur enzymes. An evolutionary origin that involves a mineral beginning and the stepwise refinement of catalytic function in response to selective pressure.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3
  • Surface Chemistry of Iron-Sulfur Minerals

    The exposure of pyrite surfaces to energetic particle beams creates an activated surface that is capable of facilitating the reduction of nitrogen molecules to ammonia. Experimental results and complementary theoretical calculations indicates that the exposure of pyrite surfaces creates anomalously reduced iron atoms. The chemical state of the surface iron atoms is somewhat similar to iron in the active center of several key enzymes. The triple bond in dinitrogen sorbed onto these reduced surface iron atoms weakens, which is a key step in the conversion to ammonia, a key reagent in the formation of amino acids on the prebiotic Earth

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 7.1 7.2
  • Nitrate and Nitrate Conversion to Ammonia on Iron-Sulfur Minerals

    Conversion of nitrate and nitrite may have contributed to the formation of ammonia—a key reagent in the formation of amino acids—on the prebiotic Earth. Results suggest that the presence of iron mono sulfide facilitates the conversion of nitrate and nitrite. Nitrite conversion is, however, much faster than the conversion of nitrate.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 7.1 7.2
  • Viral Ecology and Evolution

    This project is aimed at probing the occurrence and evolution of archaeal viruses in the extreme environments in the thermal areas in Yellowstone National Park. Viruses are the most abundant life-like entities on the planet and are likely a major reservoir of genetic diversity for all life on the planet and these studies are aimed at providing insights into the role of viruses in the evolution of early life on Earth.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2
  • The ABRC Philosophy of Astrobiology and the Origin of Life Discussion Group

    A unique feature of Montana State’s ARBC is our Philosophy of Astrobiology Focus Group. Our group consists of faculty, undergraduate, and graduate students from philosophy, history, chemistry and bio-chemistry who are interested in examining the philosophical questions that intersect with astrobiology research.

    Specifically: • What are the defining characteristics of life? • What would we look for in searching for “alternative” life forms? • What is “intelligence” and how would we know when we had found it? • How do we choose between competing theories of the origins of life? • How are emerging sciences, such as astrobiology, different from mature sciences? • What are the social implications of discovering life on another planet or, alternatively, for failing to find life? • What are the ethical obligations of scientists in conducting research on other planets? • How should we assess potential environmental and health risks associated with astrobiological research?

  • BioInspired Mimetic Cluster Synthesis: Bridging the Structure and Reactivity of Biotic and Abiotic Iron-Sulfur Motifs

    Bioinspired synthetic approaches are being utilized to bridge the gap between Fe-S minerals and highly evolved biological Fe-S metalloenzymes. Biology builds complex Fe-S clusters by first synthesizing standard Fe-S clusters and then modifying them through radical chemistry catalyzed by radical SAM enzymes. In an effort to examine hypothetical early biocatalysts, we probing simple Fe-S motifs capable of coordinating Fe-S clusters in aqueous solutions that can initiate radical chemistry.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3 3.4 7.1 7.2
  • The Subglacial Biosphere – Insights Into Life-Sustaining Strategies in an Extraterrestrial Analog Environment

    Sub-ice environments are prevalant on Earth today and are likely to have been more prevalent the Earth’s past during episodes of significant glacial advances (e.g., snow-ball Earth). Numerous metabolic strategies have been hypothesized to sustain life in sub-ice environments. Common among these hypotheses is that they are all independent of photosynthesis, and instead rely on chemical energy. Recently, we demonstrated the presence of an active assemblage of methanogens in the subglacial environment of an Alpine glacier (Boyd et al., 2010). The distribution of methanogens is narrowly constrained, due in part to the energetics of the reactions which support this functional class of organism (namely carbon dioxide reduction with hydrogen and acetate fermentation). Methanogens utilize a number of metalloenzymes that have active site clusters comprised of a unique array of metals. During the course of this study, we identified other features that were suggestive of other active and potentially relevant metabolic strategies in the subglacial environment, such as nitrogen cycling. The goals of this project are 1) identifying a suite of biomarkers indicative of biological CH4 production 2). quantifying the flux of CH4 from sub-ice systems and 3). developing an understanding how life thrives at the thermodynamic limits of life. This project represents a unique extension of the ABRC and bridges the research goals of several nodes, namely the JPL-Icy Worlds team and the ASU-Follow the Elements team.

    ROADMAP OBJECTIVES: 2.1 2.2 5.1 5.2 5.3 6.1 6.2 7.1 7.2
  • Ecology of Extreme Environments: Characterization of Energy Flow, Bioenergetics, and Biodiversity in Early Earth Analog Ecosystems

    The distribution of organisms and their metabolic functions on Earth is rooted, at least in part, to the numerous adaptive radiations that have resulted in the ability to occupy new ecological niches through evolutionary time. Such responses are recorded in extant organismal geographic distribution patterns (e.g., habitat range), as well as in the genetic record of organisms. The extreme variation in the geochemical composition of present day hydrothermal environments is likely to encompass many of those that were present on early Earth, when key metabolic processes are thought to have evolved. Environments such Yellowstone National Park (YNP), Wyoming harbor >12,000 geothermal features that vary widely in temperature and geochemical composition. Such environments provide a field laboratory for examining the tendency for guilds of organisms to inhabit particular ecological niches and to define the range of geochemical conditions tolerated by that functional guild (i.e., habitat range or zone of habitability). In this aim, we are examining the distribution and diversity of genes that encode for target metalloproteins in YNP environments that harbor geochemical properties that are thought to be similar to those that characterize early Earth. Using a number of newly developed computational approaches, we have been able to deduce the primary environmental parameters that constrain the distribution of a number of functional processes and which underpin their diversity. Such information is central to constraining the parameter space of environment types that are likely to have facilitated the emergence of these metal-based biocatalysts.

    ROADMAP OBJECTIVES: 3.2 3.3 3.4 4.1 4.2 5.1 5.2 5.3
  • Molecular Evolution: A Top Down Approach to Examine the Origin of Key Biochemical Processes

    The emergence of metalloenzymes capable of activating substrates such as CO, N2, and H2, were significant advancements in biochemical reactivity and in the evolution of complex life. Examples of such enzymes include [FeFe]- and [NiFe]-hydrogenase that function in H2 metabolism, Mo-, V-, and Fe-nitrogenases that function in N2 reduction, and CO dehydrogenases that function in the oxidation of CO. Many of these metalloenzymes have closely related paralogs that catalyze distinctly different chemistries, an example being nitrogenase and its closely related paralog protochlorophyllide reductase that functions in the biosynthesis of bacteriochlorophyll (photosynthesis). While the amino acid composition of these closely related paralogs are often quite similar, their biochemical reactivity and substrate specificity are often very different. This phenomenon is a direct consequence of the composition and molecular structure of the active site metallocluster, which requires a number of accessory proteins to synthesize. By specifically focusing on the origin and subsequent evolution of these metallocluster biosynthesis proteins in relation to paralogous proteins that have left clear evidence in the geological record (photosynthesis and the rise of O2), we have been able to obtain significant insight into the origin and evolution of these functional processes, and to place these events in evolutionary time.

    The genomes of extant organisms provide detailed histories of key events in the evolution of complex biological processes such as CO, N2, and H2 metabolism. Advances in sequencing technology continue to increase the pace by which unique (meta)genomic data is being generated. This now makes it possible to seamlessly integrate genomic information into an evolutionary context and evaluate key events in the evolution of biological processes (e.g., gene duplications, fusions, and recruitments) within an Earth history framework. Here we describe progress in using such approaches in examining the evolution of CO, N2, and H2 metabolism.

    ROADMAP OBJECTIVES: 3.2 4.1 5.1
  • Radical SAM Chemistry and Biological Ligand Accelerated Catalysis

    A number of key reactions in biological systems are catalyzed by iron-sulfur enzymes. Iron-sulfur clusters in biology have a number of features in common with iron-sulfur minerals and their derivatives. We are using iron sulfur motifs as a model system to understand how chemistry in the abiotic mineral world was incorporated into biology on a path to the origin of life. We have found that iron-sulfur motifs in biology are synthesized and modified by reactions and mechanisms that we envision minerals could have been modified on the early prebiotic Earth. The results have had a profound impact on our ability to understand a stepwise trajectory from the nonliving to the living Earth.

    ROADMAP OBJECTIVES: 3.1 3.2 3.3
  • Reactivity of Pyrite Surfaces With Thiomolybdate as Sorbate

    Sorption of a sulfur-molybdenum compound onto pyrite surfaces leads to an enhance capability of pyrite to facilitate the conversion of dinitrogen to ammonia, a key reagent in the formation of amino acids on the prebiotic Earth. The structure and chemical environment of the molybdenum-sulfur surface compound is thought to be similar to molybdenum-sulfur compounds embedded in enzymes, where these compounds facilitate the conversion of dinitrogen to ammonia.