First β-hairpin β-helix peptide

An unprecedented peptide structure-a cyclic β-hairpin β-helix (shown, with side chains)-has been designed, synthesized, and characterized by Thomas D. Clark and Christopher Brown of the Naval Research Laboratory, Washington, D.C., and Mallika Sastry and Gerhard Wagner of Harvard Medical School (J. Am. Chem. Soc., DOI: 10.1021/ja062737f). β-Helices are formed by peptides composed of alternating d- and l-amino acids and are stabilized by β-sheet-type hydrogen bonding. The antibiotic gramicidin A is a naturally occurring β-helical peptide, and several attempts have been made to synthesize similar structures, but previous efforts resulted in single- and double-stranded helical mixtures. Now, Clark and coworkers have solved that problem by tying together two appropriate peptide strands into a cyclic structure with β-hairpin ends. Such β-hairpin β-helices could serve "as structural templates for a variety of potential applications in bioorganic chemistry, from new transmembrane ion channels to new ligands for macromolecular targets such as DNA to building blocks for new protein architectures," Clark says.