CHARACTERIZATION OF BETA-BEND RIBBON SPIRAL FORMING PEPTIDES USING ELECTRONIC AND VIBRATIONAL CD

Terminally blocked (L-Pro-Aib)(n) and Aib-(L-Pro-Aib)(n) sequential ol igopeptides are known to form right-handed beta-bend ribbon spirals un der a variety of experimental conditions. Here we describe the results of a complete CD and ir characterization of this subtype of 3(10)-hel ical structure. The electronic CD spectra were obtained in solvents of different polarity in the 260-180 nm region. The vibrational CD and F ourier transform ir (FTIR) spectra were measured in deuterochloroform solution in the amide I and amide II (1750-1500 cm(-1)) regions. The c ritical chain length for full development of the beta-bend ribbon spir al structure is found to be five to six residues. Spectral effects rel ated to concentration-induced stabilization of the structures of the l onger peptides were seen in the resolution-enhanced FTIR spectra. Comp arison to previous studies of (Aib)(n) and (Pro)(n) oligomers indicate that the low frequency of the amide I mode is due to the interaction of secondary and tertiary amide bonds and not to a strong difference i n conformation from a regular 3(10)-helix. (C) 1995 John Wiley and Son s, Inc.