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 m ainly from pairwise comparisons of mesophilic and thermophilic structures a nd has often yielded conflicting results. Interpretation of these results w ould be enhanced by knowing the normal range of features found for mesophil ic proteins. In order to provide the average and distribution values of str uctural features among similar mesophilic proteins, we compared the amino a cid composition, solvent accessible surface area, hydrogen bonds, number of ion pairs, and thermal factors of 22 structures of alpha/beta barrel glyco syl 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 mesoph ilic proteins and illustrates the difficulty of making pairwise comparisons of mesophiles to thermophiles where differences for individual proteins ma y be within the normal range for the group. In comparing mesophiles to ther mophiles as a group, we find that thermophilic structures have fewer glycin es in a particular region of the structure and higher thermal factors at ro om temperature. These results suggest the basis for thermostability may be related to protein motion rather than to static features of protein structu re. (C) 2000 Elsevier Science B.V. All rights reserved.