CONFORMATIONAL-ANALYSIS OF THE BACKBONE-DEPENDENT ROTAMER PREFERENCESOF PROTEIN SIDE-CHAINS

Amino acids have sidechain rotamer preferences dependent on the backbo ne dihedral angles phi and psi. These preferences provide a method for rapid structure prediction which is a significant improvement over ba ckbone-independent rotamer libraries. We demonstrate here that simple arguments based on conformational analysis can account for many of the features of the observed backbone dependence of the sidechain rotamer s. Steric repulsions corresponding to the 'butane' and 'syn-pentane' e ffects make certain conformers rare, as has been observed experimental ly.