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Structural basis for organohalide respiration

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Science  24 Oct 2014:
Vol. 346, Issue 6208, pp. 455-458
DOI: 10.1126/science.1258118

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How bacteria break down organohalides

Anaerobic bacteria can break down a range of organohalide pollutants. To do so, they use unusual reductive dehalogenase enzymes that remove the halogen ion from the molecule, making the pollutants less toxic. Bommer et al. describe x-ray crystal structures of one such enzyme from Sulfurospirillum multivorans (see the Perspective by Edwards). Vitamin B12, present near the substrate binding site, catalyzes the reduction of trichloroethylene in concert with two iron-sulfur clusters. The structures provide mechanistic clues for how to engineer enzymes to recognize other pollutants.

Science, this issue p. 455; see also p. 424

Abstract

Organohalide-respiring microorganisms can use a variety of persistent pollutants, including trichloroethene (TCE), as terminal electron acceptors. The final two-electron transfer step in organohalide respiration is catalyzed by reductive dehalogenases. Here we report the x-ray crystal structure of PceA, an archetypal dehalogenase from Sulfurospirillum multivorans, as well as structures of PceA in complex with TCE and product analogs. The active site harbors a deeply buried norpseudo-B12 cofactor within a nitroreductase fold, also found in a mammalian B12 chaperone. The structures of PceA reveal how a cobalamin supports a reductive haloelimination exploiting a conserved B12-binding scaffold capped by a highly variable substrate-capturing region.

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