DOES THE EDGE-TO-FACE INTERACTION BETWEEN AROMATIC RINGS OCCUR IN CYCLOLINOPEPTIDE-A ANALOGS

We measured H-1-NMR, fluorescence and CD spectra of cyclolinopeptide A (CLA), its tyrosine analogues with each or both phenylalanines substi tuted by tyrosine (c-[LeuIleIleLeuValProProTyrPhe], c-[LeuIleIleLeuVal ProProPheTyr] and c-[LeuIleIleLeuValProProTyrTyr]), and their linear c ounterparts with the starting sequence Leu-Ile-Ile-Leu-Val-Pro-Pro-Phe -Phe (LA). It follows from CD spectra that the conformations of all cy clic peptides are similar to that of CLA; the conformations of linear peptides are more diversified, with the conformation of [Tyr9]LA being most similar to CLA. NMR studies suggest that aromatic rings in cycli c peptides are situated perpendicular to each other, manifesting edge- to-face pairing. Accordingly, the residue in position 9 is shielded (' edge'), and a residue in position 8 is the shielding one ('face'). Thi s effect is not present in the case of linear peptides. Fluorescence q uantum yields were much lower for cyclic peptides than for linear ones , indicating the interaction of closely located aromatic chromophores. Those quantum yields depend on the relative position of Tyr in the pe ptide chain. Another factor influenced by the position in the peptide chain is the optical activity of aromatic side chains (optically activ e in position 8, inactive in position 9). This phenomenon could be exp lained by the differences in the side-chain conformation of both aroma tic residues. (C) Munksgaard 1994.