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Radical-mediated dehydration reactions in anaerobic bacteria

Lookup NU author(s): Professor Bernard Golding

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Abstract

Most dehydratases catalyse the elimination of water from β-hydroxy ketones, β-hydroxy carboxylic acids or β-hydroxyacyl-CoA. The electron-withdrawing carbonyl functionalities acidify the α-hydrogens to enable their removal by basic amino acid side chains. Anaerobic bacteria, however, ferment amino acids via α- or γ-hydroxyacyl-CoA, dehydrations of which involve the abstraction of a β-hydrogen, which is ostensibly non-acidic (pK ca. 40). Evidence is accumulating that β-hydrogens are acidified via transient conversion of the CoA derivatives to enoxy radicals by one-electron transfers, which decrease the pK to 14. The dehydrations of (R)-2-hydroxyacyl-CoA to (E)-2-enoyl-CoA are catalysed by heterodimeric [4Fe-4S]-containing dehydratases, which require reductive activation by an ATP-dependent one-electron transfer mediated by a homodimeric protein with a [4Fe-4S] cluster between the two subunits. The electron is further transferred to the substrate, yielding a ketyl radical anion, which expels the hydroxyl group and forms an enoxy radical. The dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA involves a similar mechanism, in which the ketyl radical anion is generated by one-electron oxidation. The structure of the FAD- and [4Fe-4S]-containing homotetrameric dehydratase is related to that of acyl-CoA dehydrogenases, suggesting a radical-based mechanism for both flavoproteins. Copyright © Walter de Gruyter 2005 All Rights Reserved.


Publication metadata

Author(s): Buckel W, Martins BM, Messerschmidt A, Golding BT

Publication type: Review

Publication status: Published

Journal: Biological Chemistry

Year: 2005

Volume: 386

Issue: 10

Pages: 951-959

ISSN (print): 1431-6730

ISSN (electronic): 1437-4315

URL: http://dx.doi.org/10.1515/BC.2005.111

DOI: 10.1515/BC.2005.111

PubMed id: 16218867


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