Protein Engineering, Vol. 15, No. 8, 651-657,
August 2002
© 2002 Oxford University Press
Stability and amino acid preferences of type VIII reverse turn: the most common turn in peptides?
Department of Chemistry, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland
Free energies of the 
rß and ßß conformations of 14 tetrapeptides, based on the sequence SALN and protein X-ray structures, were calculated using molecular dynamics simulations and MM-PBSA calculations. The conformations of five of the tetrapeptides were also studied. SALN has been earlier shown by molecular dynamics simulations and NMR spectroscopy to have a tendency to form an rß turn. The gas-phase energy of the molecular mechanical force field (CHARMM), the electrostatic and non-polar solvation free energies and solute entropies were used to explain the free energy differences of the , ßß and rß conformations of the peptides. The rß conformation of SALN and SATN was predicted to be slightly more stable than the extended conformation (ßß), in agreement with experimental results. The SALN mutants SAIN, SAVN, SATN, SSIN and MSHV, were also predicted to be potential rß turn-forming peptides. We report also revised positional potentials for the type VIII turn, based on a non-homologous set of protein structures. This protein databank analysis confirms the main results of the earlier analyses and reveals several new amino acid residues with a significant positional preference. The results of this work led us to suggest that the rß turn may be the most common turn type in peptides. Such turns may be readily formed in aqueous solution and thereby play important roles in the protein folding process by serving as an initiation point for structure formation.