Presented as part of a commemorative issue for Wolfgang Kiefer on the occasion of his 65th birthday.
The conformations adopted by the octamer peptide (AAKA)2 in aqueous solution probed by FTIR and polarized Raman spectroscopy†
Article first published online: 12 JAN 2006
Copyright © 2006 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy
Special Issue: Commemorative Issue: for Wolfgang Kiefer on the Occasion of his 65th Birthday
Volume 37, Issue 1-3, pages 248–254, January - March 2006
How to Cite
Measey, T. and Schweitzer-Stenner, R. (2006), The conformations adopted by the octamer peptide (AAKA)2 in aqueous solution probed by FTIR and polarized Raman spectroscopy. J. Raman Spectrosc., 37: 248–254. doi: 10.1002/jrs.1455
- Issue published online: 12 JAN 2006
- Article first published online: 12 JAN 2006
- Manuscript Accepted: 19 JUL 2005
- Manuscript Received: 27 APR 2005
- National Science Foundation. Grant Number: MCB-0318749.
- ACS-Petroleum Research Funds. Grant Number: PRF # 37406-AC.
- polyproline II;
- polarized Raman spectroscopy;
- FTIR spectroscopy;
- alanine-based peptides
In an effort to further elucidate the chain length dependence of the poly-L-proline 31 helical structure (PPII) in short alanine-based polypeptides, we utilize FTIR, isotropic and anisotropic Raman, and electronic circular dichroism (ECD) spectroscopies to probe the amide I′ band of the unblocked octamer H-Ala-Ala-Lys-Ala-Ala-Ala-Lys-Ala-OD in D2O. Our results are in disagreement with recent notions suggesting that the 31 helical structure increases with an increase in the number of alanine residues.1, 2 Simulations of the spectra were carried out and found to best reproduce experimental spectra using parameters that suggest a 40/60% PPII/β-strand (ßs) mixture. The amount of PPII in the octamer is found to be significantly lower than what was determined for unblocked alanine-based peptides of comparable or even larger size. This is confirmed by the relatively weak ECD minimum and maximum at ∼195 and ∼220 nm, respectively, for the octamer relative to tri- and tetraalanine.3 In this paper we also address a recent issue concerning the validity of the delocalized character of the amide I mode in unfolded polypeptides containing a significant amount of PPII structure. We conclude that experimental evidence strongly supports the vibrational coupling model used to interpret the amide I mode in unfolded polypeptides. Copyright © 2006 John Wiley & Sons, Ltd.