Abstract
This chapter describes the nature and conformation of peptide bond. One of the most fascinating aspects of the unique nature of the peptide bond is the ability of nascent biosynthetic peptide chains to fold spontaneously into the complex three-dimensional structures, which are characteristic of proteins. The chapter presents a solution conformation for oxytocin that revealed the presence of a type II β-turn involving the sequence -Tyr-Ile-Gln-Asn- within the 20-membered cyclic moiety of the hormone. The chain is folded back into an antiparallel pleated sheat conformation with the disulfide bridge closing the ring and stabilizing the structure. The backbone NH of asparagine-5 is hydrogen bonded to the C=O of tyrosine-2 and provides additional intramolecular stabilization. The CONH2-terminal tail moiety forms a second β-turn, comprising residues -Cys-Pro-Leu-Gly-, which folds the tail over one side of the ring and is stabilized by another hydrogen bond between the NH of the leucine-8 and the side chain C=O of the asparagine-5 residues. All peptide bonds are of trans configuration, including the Cys–Pro bond. Similar but not identical conformations have been deduced for lysine-vasopressin, arginine-vasopressin, and arginine-vasotocin.
Published Version
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