Evolutionary drivers of thermoadaptation in enzyme catalysis

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 enzymes (3-5). Further, we have extended this analysis to account for curved Eyring plots for biological processes at ecosystem scales (6). More recently, we have directly measured ∆Cp for the binding of transition state (TS) analogues to the cognate enzyme and shown congruence between ∆Cp (for TS-analogue binding) and ∆Cp^‡ for the enzyme-catalyzed reaction (7).

References
1. V. Nguyen C. Wilson, M. Hoemberger, J.B. Stiller, R.V. Agafonov, S. Kutter, J. English, D.L. Theobald, D. Kern, Evolutionary drivers of thermoadaptation in enzyme catalysis. Science. 355, 289–294 (2017).
2. R. Wolfenden, Massive thermal acceleration of the emergence of primordial chemistry, the incidence of spontaneous mutation, and the evolution of enzymes. J Biol Chem. 289, 30198–30204 (2014).
3. J. K. Hobbs, W. Jiao, A.D. Easter, E.J. Parker, L.A. Schipper, V.L. Arcus, Change in heat capacity for enzyme catalysis determines temperature dependence of enzyme catalyzed rates. ACS Chem. Biol. 8, 2388–2393 (2013).
4. V. L. Arcus, E.J. Prentice, J.K. Hobbs, A.J. Mulholland, M.W. Van der Kamp, C.R. Pudney, E.J. Parker, L.A. Schipper, On the temperature dependence of enzyme-catalyzed rates. Biochemistry. 55, 1681–1688 (2016).
5. V. L. Arcus, C. R. Pudney, Change in heat capacity accurately predicts vibrational coupling in enzyme catalyzed reactions. FEBS Lett. 589, 2200–2206 (2015).
6. L. A. Schipper, J. K. Hobbs, S. Rutledge, V. L. Arcus, (2014) Thermodynamic theory explains the temperature optima of soil microbial processes and high Q10 values at low temperatures. Global Change Biol. 20, 3578–3586.
7. R. S. Firestone, S. A. Cameron, J. M. Karp, V. L. Arcus, V. L. Schramm, Heat capacity changes for transition-state analogue binding and catalysis with human 5'-methylthioadenosine phosphorylase. ACS Chem. Biol. (2016), doi:10.1021/acschembio.6b00885.