Theoretical conformational analysis of disulfide-linked tetrapeptides Ac-Cys-Pro-D-Xaa-Cys-NHMe having hydrophobic D-Xaa amino-acid residues

Summary

Theoretical conformational analysis was carried out for four disulfide-linked tetrapeptides Ac-Cys-Pro-D-Xaa-Cys-NHMe(D-Xaa= D-Val, D-Phe, D-Leu, and D-norleucine) using ECEPP and optimization procedure for investigating how the stabilities of the β-bend conformation at D-Xaa-Pro portion are affected by branching and bulkiness of hydrophobic side-chain groups of D-Xaa residue. Calculated results indicate that cyclic Ac-Cys-Pro-D-Xaa-Cys-NHMe commonly have a dominant character taking type II β-bend at the Pro-D-Xaa portion and also show fairly good agreement with experimental results of the NMR spectroscopy for a tetrapeptide Ac-Cys-Pro-D-Val-Cys-NH2. It is shown that the Ala-residue approximation is also a reasonable method to investigate the basic local conformational character of the Cys-Pro-D-Xaa-Cys sequence as well as that of the Cys-Pro-Xaa-Cys one. Moreover, it is suggested that the disulfide-linked tetrapeptides Ac-Cys-Pro-D-Xaa-Cys-NHMe are good candidates of the simple standard molecules for investigating the spectroscopic characters related to type II β-bend conformations.