Atomic displacement parameters of homologous proteins: Conservation of dynamics

Atomic displacement parameters (ADPs) obtained from highresolution refinement of protein structures represent the mean square displacement of protein atoms from their centroid positions. They contain information regarding the flexibility of the polypeptide. Comparative analysis of the ADPs in homologous proteins shows that the local flexibility of the polypeptide is not correlated to the mutability of the segment. The flexible and rigid regions in the threedimensional fold of proteins remain largely conserved during the course of evolution. In related proteins, the variation in the flexibility of a given segment is only weakly correlated to the variation of the amino acid sequence at the corresponding positions. These results illustrate that the relationship between sequence and dynamics has degeneracy similar to that of sequence and three-dimensional structure. The observations are consistent with the importance of protein flexibility to protein function.