CORRELATION BETWEEN SIDE-CHAIN MOBILITY AND CONFORMATION IN PROTEIN STRUCTURES

Thermal factors of protein atoms as determined by X-ray crystallograph ic techniques show a tendency to be larger in side chains with unfavou rable local conformations rather than in those displaying conformation al energy minima. It follows that side chain atoms are more mobile if they are in a non-rotameric configuration and that the stereochemistry of protein structures cannot be fully assessed or simulated without c onsideration of thermal factors that monitor flexibility in various re gions of the protein. The observations should also prove useful in pro tein folding and design.