Unusual β-sheet periodicity in small cyclic peptides

Abstract
Cyclic peptide homologs of gramicidin S containing 6, 8, 10, 12, 14 and 16 residues were synthesized and characterized using circular dichroism (CD) and 1H NMR spectroscopy. Based on the three-dimensional structures generated from these data we have found strong evidence of a periodic sequence-length dependence on β-sheet content. In particular, peptides of length 6, 10 and 14 residues exhibit a high β-sheet content, while peptides of 8, 12 and 16 residues appear to exist as random coils. This unusual β-sheet periodicity may have important implications in our understanding of β-sheet formation and in the design of constrained β-sheet and β-hairpin mimics.