A Designed β -Hairpin Peptide in Crystals

β -hairpin structures have been crystallographically characterized only in very short acyclic peptides, in contrast to helices. The structure of the designed β -hairpin, t-butoxycarbonyl-Leu-Val-Val-D-Pro-Gly-Leu-Val-Val-OMe in crystals is described. The two independent molecules of the octapeptide fold into almost ideal β -hairpin conformations with the central D-Pro-Gly segment adopting a Type II′β -turn conformation. The definitive characterization of a β -hairpin has implications for de novo peptide and protein design, particularly for the development of three- and four-stranded β -sheets.