Energy-conformation studies of frequency of beta-turns in tetrapeptide sequences.

The optimized energies of seven beta-bends, repeating C5 and C7, and right- and left-handed alpha-helical conformations for each of eight tetrapeptides have been computed using empirical methods. Eight tetramers were selected: four helix-forming sequences with hydrophobic residues such as Val, Leu, Ile and Trp, and four helix-breaking sequences with hydrophilic residues such as Asp, Asn and Ser, as determined by their frequency of occurrence in beta turns in proteins. Analysis of the optimized conformations with energies less than or equal to 2.1 kcal/mol from the absolute minimum energy conformer for each tetramer reveals a correlation between low-energy conformations and those predicted from observed protein structures. These results show that energy calculations on small peptide fragments may be usefulin predicting protein structure.