Investigation of the Conformations of Four Tetrapeptides by Nuclear Magnetic Resonance and Circular Dichroism Spectroscopy, and Conformational Energy Calculations

Proton nuclear magnetic resonance and circular dichroism studies were carried out on aqueous solutions of the tetrapeptide Asp-Lys-Thr-Gly (which appears as a bend at residues 35-38 of alpha-chymotrypsin) and its sequence variants Gly-Thr-Asp-Lys, Asp-Lys-Gly-Thr, and Lys-Thr-Gly-Asp; the N and C termini of all four tetrapeptides were blocked with CH3CO and NHCH3 groups, respectively. The spectroscopic data suggest that bend conformations may exist, to some extent, among the distributions of conformations in the first, third, and fourth, but not in the second, tetrapeptide. This result is consistent with empirical probabilities for the prediction of bend conformations in proteins. Conformational energy calculations on these four tetrapeptides support the indications from the experimental data. It thus appears that, because of short-range interactions, the tendency toward bend formation exists in short peptides, provided that both the composition and amino acid sequence are energetically favorable for bend formation.