Investigation of various conformations of HCO-Gly-L-Val-Gly-NH_2 tripeptide in elastin: Ab initio and DFT calculations

摘要

In this reaserch, conformations of the tripeptide model HCO-Gly-L-Val-Gly-NH_2 of parent elastin-mimetic polypeptide by rotating the valine sidechain and backbone torsional angles are discussed. All calculations were performed with using Gaussian 03 program employing B_3LYP level with 6-31G(d) basis set., Optimized structures were obtained for backbone torsional angles conformers, at 30° intervals, from 0° to 360°, of (g-) conformer. When Φ_1, Ψ_1, Φ_3 and Ψ_3 were 180°, were found lowest energy, but, when valine torsional angles Φ_2Ψ_2 were (180°,-120°) and (150°,180°), respectively, were found lowest energy therefore, backbone dihedral angles lead to less values of 180° by larger sidechain groups. Also optimized structures, energes, valine dihedral angles were obtained for the nine possible minima present on the Ramachandran map in g+,g- and anti conformations. β_Lα_Dβ_L, β_LY_Lβ_L, β_LY_Dβ_L, β_LC_Dβ_L and β_Lβ_Lβ_L conformers were found in these three states. Among studied conformations, β_L extended conformer was found highest stability. β_LC_Lβ_L conformer was absent in every three states. The dipole-dipole attraction and entropy play a role in the stabilization of certain conformers of amino acid diamides.