A meta-analysis of the activity, stability, and mutational characteristics of temperature-adapted enzymes

Abstract

Understanding the characteristics that define temperature-adapted enzymes has been a major goal of extremophile enzymology in recent decades. In the present study, we explore these characteristics by comparing psychrophilic, mesophilic, and thermophilic enzymes. Through a meta-analysis of existing data, we show that psychrophilic enzymes exhibit a significantly larger gap (Tg) between their optimum and melting temperatures compared with mesophilic and thermophilic enzymes. These results suggest that Tg may be a useful indicator as to whether an enzyme is psychrophilic or not and that models of psychrophilic enzyme catalysis need to account for this gap. Additionally, by using predictive protein stability software, HoTMuSiC and PoPMuSiC, we show that the deleterious nature of amino acid substitutions to protein stability increases from psychrophiles to thermophiles. How this ultimately affects the mutational tolerance and evolutionary rate of temperature adapted organisms is currently unknown.

Keywords: enzyme activity; enzymology; extremophiles; mutation; protein stability.

Figure 1. The activity and stability parameters of temperature-adapted enzymes

Panel (A) represents the optimum temperature for enzyme activity (T_opt), while (B) shows the melting temperatures (T_m) of the individual enzymes. Panel (C) shows the temperature gap between T_opt and T_m, denoted as T_g. The individual data points for psychrophiles are represented by circles, mesophiles by squares, and the thermophiles by triangles. All data points are plotted with the mean ± the SEM. * represent the statistical significance results from Tukey’s multiple comparisons tests for panels (A,B) and Dunnett’s T3 multiple comparisons tests for panel (C) (** = P<0.01, *** = P<0.001, **** = P<0.0001, ns = not significant).

Figure 2. The effects of mutations to temperature-adapted enzymes

Panel (A) shows a representative protein stability curve expressed as its Gibbs free energy of folding (ΔG_f) across temperature. The stability curve exhibits two melting points where it crosses the x-axis, and a peak of stability where the curve has its most negative y value. Horizontal and vertical arrows represent the changes to protein stability predicted by HoTMuSiC and PoPMuSiC respectively (ΔT_m and ΔΔG_f). Panel (B) shows the ΔT_m predicted by HoTMuSiC to enzymes from psychrophiles, mesophiles, and thermophiles as a result of single amino acid mutations. Panel (C) shows the ΔΔG_f predicted by PoPMuSiC to enzymes from psychrophiles, mesophiles, and thermophiles. All data points are plotted with the mean ± the SEM. * represent the statistical significance results from Dunnett’s T3 multiple comparisons tests for panel (B) and Tukey’s multiple comparisons tests for panel (C) (* = P<0.05, ** = P<0.01, *** = P<0.001, ns = not significant).