Revisiting the correlation between proteins' thermoresistance and organisms' thermophilicity

The possibility to rationally design protein mutants that remain structured and active at high temperatures strongly depends on a better understanding of the mechanisms of protein thermostability. Studies devoted to this issue often rely on the living temperature (T-env) of the host organism rather than on the melting temperature (T-m) of the analyzed protein. To investigate the scale of this approximation, we probed the relationship between T-m and T-env on a dataset of 127 proteins, and found a much weaker correlation than previously expected: the correlation coefficient is equal to 0.59 and the regression line is T-m approximate to 42.9 degrees C + 0.62T(env). To illustrate the effect of using T-env rather than T-m to analyze protein thermoresistance, we derive statistical distance potentials, describing Glu-Arg and Asp-Arg salt bridges, from protein structure sets with high or low T-m or T-env. The results show that the more favorable nature of salt bridges, relative to other interactions, at high temperatures is more clear-cut when defining thermoresistance in terms of T-m. The T-env-based sets nevertheless remain informative.