Growth temperature and relative stabilities of proteins

This vignette demonstrates an analysis of the relative stabilities of 24 carboxylases from model organisms that grow optimally at different temperatures. In the chemical thermodynamic model, changes in both temperature and oxidation potential influence the relative stabilities of the proteins with an overall progression that fits with the growth temperatures of the organisms. The calculations supporting this study are presented using a series of equilibrium activity diagrams constructed using CHNOSZ. First, equilibrium activity diagrams as a function of either temperature or log aH2 (at constant values of the other variable) show that both variables contribute significantly to the relative stabilities of the proteins. Second, an equilibrium predominance diagram is used to formulate an expression for log aH2 as a function of temperature that crosses the protein stability fields in order of increasing growth temperature of the organism. Third, equilibrium activity and chemical species richness diagrams based on this function show pattern that mirrors the natural growth temperature of the organism. The final piece of code produces an animated series of rank-abundance diagrams for the proteins as both temperature and log aH2 are increased.