Protein thermal stability: hydrogen bonds or internal packing?

Thermally stable proteins are of interest for several reasons. They can be used to improve the efficiency of many industrial processes and provide insight into the general mechanisms of protein folding and stabilization. Comparison of tertiary structural properties of several protein families with members of different thermostability should help to delineate the role of individual factors in achieving stability at high temperature. In this work, 16 protein families with at least one known thermophilic and one known mesophilic tertiary structure were examined for the number and type of hydrogen bonds and salt links, polar surface composition, internal cavities and packing densities, and secondary structural composition. The results show a consistent increase in the number of hydrogen bonds and in polar surface area fraction with increased thermostability.