Distributions of structural features contributing to thermostability in mesophilic and thermophilic alpha/beta barrel glycosyl hydrolases.

Analysis of the structural basis for thermostability in proteins has come mainly from pairwise comparisons of mesophilic and thermophilic structures and has often yielded conflicting results. Interpretation of these results would be enhanced by knowing the normal range of features found for mesophilic proteins. In order to provide the average and distribution values of structural features among similar mesophilic proteins, we compared the amino acid composition, solvent accessible surface area, hydrogen bonds, number of ion pairs, and thermal factors of 22 structures of alpha/beta barrel glycosyl hydrolases. These distributions are then compared to values from seven alpha/beta barrel glycosyl hydrolases from thermophilic organisms. We find that the distribution of each structural feature is broad within the mesophilic proteins and illustrates the difficulty of making pairwise comparisons of mesophiles to thermophiles where differences for individual proteins may be within the normal range for the group. In comparing mesophiles to thermophiles as a group, we find that thermophilic structures have fewer glycines in a particular region of the structure and higher thermal factors at room temperature. These results suggest the basis for thermostability may be related to protein motion rather than to static features of protein structure.