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Evolutionary drivers of thermoadaptation in enzyme catalysis

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Science  20 Jan 2017:
Vol. 355, Issue 6322, pp. 289-294
DOI: 10.1126/science.aah3717

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  • RE: Enzyme evolution and heat capacity changes for enzyme-catalyzed reactions
    • Vickery L. Arcus, Professor, University of Waikato, Hamilton, New Zealand
    • Other Contributors:
      • Adrian J. Mulholland, Professor, University of Bristol, Bristol, U.K.
      • Joanne K. Hobbs, Research Fellow, University of Victoria, Victoria, Canada
      • Marc W. Van der Kamp, Research Fellow, University of Bristol, Bristol, U.K.
      • Christopher R. Pudney, Lecturer, University of Bath, Bath, U.K.
      • Emily J. Parker, Professor, Victoria University of Wellington, Wellington, New Zealand
      • Louis A. Schipper, Professor, University of Waikato, Hamilton, New Zealand

    The mechanisms underlying adaptation of enzymes to different environmental temperatures is a central question in evolutionary biology. Kern and colleagues (1) document this for adenylate kinase for which product release is rate determining. They find a small change in heat capacity for reaction (∆Cp^‡) from approximately −1 kJ.mol−1.K−1 towards zero, on progression from hotter to cooler temperatures. In agreement with Wolfenden (2), they argue that this reduces the enthalpy of activation (∆H^‡) as temperature drops.

    In their concluding paragraph they state that “∆Cp^‡ as a source of nonlinear Eyring plots had only been measured for non-enzymatic reactions (31) and protein folding (23).” This is incorrect as we have previously demonstrated curved Eyring plots for enzymes including a stabilized mutant of barnase and several mutants of the glucosidase MalL and we have ascribed this curvature to ∆Cp^‡ (3). Importantly, we are able to separate the denaturation rate (ku) from the catalytic rates (kcat & kcat/Km) by explicitly measuring all three parameters (ku, kcat & Km) at different temperatures. Thus, our curved Eyring plots are independent of denaturation. We have used molecular dynamics to explain the differences between ∆Cp^‡ for wildtype MalL and two mutant MalL enzymes (3) and we have developed Macromolecular Rate Theory (MMRT), which explains the temperature-rate data we have observed experimentally (4) and which is consistent with data for very many enz...

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    Competing Interests: None declared.