A sequence‐dependent 1H‐NMR study on the formation of β‐turns in tetrapeptides containing charged residues

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Abstract
The importance of side‐chain charge interactions in the formation of β‐turns was studied. Sixteen protected NAc‐tetrapeptide amides were studied, namely the variants of DEKS: NEKS, EEKS, DDKS, DQKS, NQKS, DERS, NERS, EERS, DDRS, NDRS, DQRS, and DKES. Three tetrapeptides—NPDM, NSDM, and NDDS—were also studied as they have a high probability of forming β‐turns, based on statistical predictions. The results indicate that a small proportion of type I β‐turn exists in solutions of DEKS and DERS in methanol/ water (60/40), while NEKS has an even smaller population of this turn. The other tetrapeptides are present in solution only in the extended conformation. These results clearly show the importance of the salt bridge between the side chains of K2 and E3 or R2 and E3, as well as the importance of the charge on the side chain of the first residue in stabilizing the β‐turn. The relevance of statistical predictions for β‐turns in short peptides is discussed.