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26 Publications

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    05/02/17 | Discovery of chemoautotrophic symbiosis in the giant shipworm Kuphus polythalamia (Bivalvia: Teredinidae) extends wooden-steps theory
    Distel DL, Altamia MA, Lin Z, Shipway JR, Han A, Forteza I, Antemano R, Limbaco MG, Tebo AG, Dechavez R, Albano J, Rosenberg G, Concepcion GP, Schmidt EW, Haygood MG
    Proceedings of the National Academy of Sciences. 05/2017;114:E3652–E3658. doi: 10.1073/pnas.1620470114

    Certain marine invertebrates harbor chemosynthetic bacterial symbionts, giving them the remarkable ability to consume inorganic chemicals such as hydrogen sulfide (H2S) rather than organic matter as food. These chemosynthetic animals are found near geochemical (e.g., hydrothermal vents) or biological (e.g., decaying wood or large animal carcasses) sources of H2S on the seafloor. Although many such symbioses have been discovered, little is known about how or where they originated. Here, we demonstrate a new chemosynthetic symbiosis in the giant teredinid bivalve (shipworm) Kuphus polythalamia and show that this symbiosis arose in a wood-eating ancestor via the displacement of ancestral cellulolytic symbionts by sulfur-oxidizing invaders. Here, wood served as an evolutionary stepping stone for a dramatic transition from heterotrophy to chemoautotrophy.The “wooden-steps” hypothesis [Distel DL, et al. (2000) Nature 403:725–726] proposed that large chemosynthetic mussels found at deep-sea hydrothermal vents descend from much smaller species associated with sunken wood and other organic deposits, and that the endosymbionts of these progenitors made use of hydrogen sulfide from biogenic sources (e.g., decaying wood) rather than from vent fluids. Here, we show that wood has served not only as a stepping stone between habitats but also as a bridge between heterotrophic and chemoautotrophic symbiosis for the giant mud-boring bivalve Kuphus polythalamia. This rare and enigmatic species, which achieves the greatest length of any extant bivalve, is the only described member of the wood-boring bivalve family Teredinidae (shipworms) that burrows in marine sediments rather than wood. We show that K. polythalamia harbors sulfur-oxidizing chemoautotrophic (thioautotrophic) bacteria instead of the cellulolytic symbionts that allow other shipworm species to consume wood as food. The characteristics of its symbionts, its phylogenetic position within Teredinidae, the reduction of its digestive system by comparison with other family members, and the loss of morphological features associated with wood digestion indicate that K. polythalamia is a chemoautotrophic bivalve descended from wood-feeding (xylotrophic) ancestors. This is an example in which a chemoautotrophic endosymbiosis arose by displacement of an ancestral heterotrophic symbiosis and a report of pure culture of a thioautotrophic endosymbiont.

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    02/08/17 | Intramolecular Photogeneration of a Tyrosine Radical in a Designed Protein
    Tebo AG, Quaranta A, Herrero C, Pecoraro VL, Aukauloo A
    ChemPhotoChem. 02/2017;1:89 – 92. doi: 10.1002/cptc.201600044

    Long‐distance biological electron transfer occurs through a hopping mechanism and often involves tyrosine as a high potential intermediate, for example in the early charge separation steps during photosynthesis. Protein design allows for the development of minimal systems to study the underlying principles of complex systems. Herein, we report the development of the first ruthenium‐linked designed protein for the photogeneration of a tyrosine radical by intramolecular electron transfer.

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    10/19/15 | Variable primary coordination environments of Cd(II) binding to three helix bundles provide a pathway for rapid metal exchange.
    Tebo AG, Hemmingsen L, Pecoraro VL
    Metallomics. 10/2015;7:1555 – 1561. doi: 10.1039/c5mt00228a

    Members of the ArsR/SmtB family of transcriptional repressors, such as CadC, regulate the intracellular levels of heavy metals like Cd(II), Hg(II), and Pb(II). These metal sensing proteins bind their target metals with high specificity and affinity, however, a lack of structural information about these proteins makes defining the coordination sphere of the target metal difficult. Lingering questions as to the identity of Cd(II) coordination in CadC are addressed via protein design techniques. Two designed peptides with tetrathiolate metal binding sites were prepared and characterized, revealing fast exchange between CdS3O and CdS4 coordination spheres. Correlation of (111m)Cd PAC spectroscopy and (113)Cd NMR spectroscopy suggests that Cd(II) coordinated to CadC is in fast exchange between CdS3O and CdS4 forms, which may provide a mechanism for rapid sensing of heavy metal contaminants by this regulatory protein.

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    01/08/15 | Artificial metalloenzymes derived from three-helix bundles.
    Tebo AG, Pecoraro VL
    Current Opinion in Chemical Biology. 01/2015;25C:65 – 70. doi: 10.1016/j.cbpa.2014.12.034

    Three-helix bundles and coiled-coil motifs are well-established de novo designed scaffolds that have been investigated for their metal-binding and catalytic properties. Satisfaction of the primary coordination sphere for a given metal is sufficient to introduce catalytic activity and a given structure may catalyze different reactions dependent on the identity of the incorporated metal. Here we describe recent contributions in the de novo design of metalloenzymes based on three-helix bundles and coiled-coil motifs, focusing on non-heme systems for hydrolytic and redox chemistry.

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    08/01/08 | Porphyrins and Metalloporphyrins at Components in Artificial Photosynthesis Research
    Tebo AG, Herrero C, Aukauloo A, Kadish KM, Smith KM, undefined , Guilard R
    Handbook of Porphyrin Science;34:196 – 233. doi: 10.1142/9789814417297_0016
    03/24/14 | Protein design: toward functional metalloenzymes.
    Yu F, Cangelosi VM, Zastrow ML, Tegoni M, Plegaria JS, Tebo AG, Mocny CS, Ruckthong L, Qayyum H, Pecoraro VL
    Chemical reviews. 03/2014;114:3495 – 3578. doi: 10.1021/cr400458x