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Molecular Mechanism of a Hotdog-Fold Acyl-CoA Thioesterase

Authors

  • Dr. David C. Cantu,

    1. Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa 50011-2230 (USA)
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  • Dr. Albert Ardèvol ,

    1. Computer Simulation and Modeling Laboratory, Parc Científic de Barcelona, 08028 Barcelona (Spain)
    2. Department of Chemistry and Applied Biosciences, ETH Zürich, USI Campus, 6900 Lugano (Switzerland)
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  • Prof. Carme Rovira ,

    1. Departament de Química Orgànica and Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, 08028 Barcelona (Spain)
    2. Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona (Spain)
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  • Prof. Peter J. Reilly

    Corresponding author
    1. Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa 50011-2230 (USA)
    • Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa 50011-2230 (USA)===

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Abstract

Thioesterases are enzymes that hydrolyze thioester bonds between a carbonyl group and a sulfur atom. They catalyze key steps in fatty acid biosynthesis and metabolism, as well as polyketide biosynthesis. The reaction molecular mechanism of most hotdog-fold acyl-CoA thioesterases remains unknown, but several hypotheses have been put forward in structural and biochemical investigations. The reaction of a human thioesterase (hTHEM2), representing a thioesterase family with a hotdog fold where a coenzyme A moiety is cleaved, was simulated by quantum mechanics/molecular mechanics metadynamics techniques to elucidate atomic and electronic details of its mechanism, its transition-state conformation, and the free energy landscape of the process. A single-displacement acid-base-like mechanism, in which a nucleophilic water molecule is activated by an aspartate residue acting as a base, was found, confirming previous experimental proposals. The results provide unambiguous evidence of the formation of a tetrahedral-like transition state. They also explain the roles of other conserved active-site residues during the reaction, especially that of a nearby histidine/serine pair that protonates the thioester sulfur atom, the participation of which could not be elucidated from mutation analyses alone.

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