A pair of pyrene groups as a conformational probe for antiparallel beta-sheet structure, formed in cyclic peptides

We have developed the utility of a pair of pyrene groups on L-1-pyrenylalanines (Pya) as a conformational probe for designed,peptides composed of alpha-helices. Here we expand the usefulness of the probing method to the antiparallel beta-sheet structure formed in cyclic peptides. A pair of Pya residues were introduced into cyclic decapeptides, gramicidin S and its analogous peptide, at various positions which were involved in antiparallel beta-sheet structures with amphiphilic character. When the two Pya residues were deployed on different beta-strands, exciton interaction in circular dichroism spectra showed that the two pyrene rings were arranged with a left-handed twist. They were orientated in a right-handed sense in the same strand. The pyrene rings showed strong excimer emission; These results demonstrate that the behaviour of the pyrene probe is coincident with the left-handed orientation of two beta-strands and the right-handed twist of a single beta-strand in natural protein structures.