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Discriminating 3 10 ‐ from α‐helices: Vibrational and electronic CD and IR absorption study of related Aib‐containing oligopeptides
Author(s) -
D. Silva R. A. Gangani,
Yasui Sritana C.,
Kubelka Jan,
Formaggio Fernando,
Crisma Marco,
Toniolo Claudio,
Keiderling Timothy A.
Publication year - 2002
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.10241
Subject(s) - chemistry , vibrational circular dichroism , amide , circular dichroism , absorption (acoustics) , fourier transform infrared spectroscopy , spectral line , absorption spectroscopy , infrared spectroscopy , fourier transform , infrared , crystallography , analytical chemistry (journal) , optics , organic chemistry , mathematical analysis , physics , mathematics , astronomy
Model peptides based on ‐(Aib‐Ala) n ‐, and (Aib) n ‐Leu‐(Aib) 2 sequences, which have varying amounts of 3 10 ‐helical character, were studied by use of vibrational and electronic circular dichroism (VCD and ECD) and Fourier transform infrared (FTIR) absorption spectroscopies to test the correlation of spectral response and conformation. The data indicate that these peptides, starting from a length of about four to six residues, predominantly adopt a 3 10 ‐helical conformation at room temperature. The longest model peptides, depending on the series, may evidence some α‐helical contribution to the spectra, while the shorter ones, with less than six residues, have much less order. The IR absorption spectra (as supported by theory) showed only small frequency changes between 3 10 ‐ and α‐helices. By contrast, solvent effects are a source of much bigger perturbations. The ECD results show that the intensity ratio for the ∼ 222‐nm to ∼ 208‐nm bands, while useful for distinguishing between these two helical types in some sequences, may have a narrower range of application than VCD. However, the VCD data presented here continue to support the proposed discrimination between α‐ and 3 10 ‐helices based on qualitative amide I and II bandshape differences. The present study shows the intensities of the 3 10 ‐helical amide I (peak‐to‐peak) to its amide II VCD to be of the same order and useful for discriminating them from α‐helices, whose amide I dominates the amide II in intensity. This qualitative result is experimentally independent of the amount of αMe‐substituted residues in the sequence. These experimental VCD results are consistent in detail with theoretical spectral simulations for Ac‐(Ala) 8 ‐NH 2 , Ac‐(Aib‐Ala) 4 ‐NH 2 , and Ac‐(Aib) 8 ‐NH 2 in 3 10 ‐ and α‐helical conformations. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 229–243, 2002