Characterizing peptide helices by site-specific coupling through use of isotopic labeling
Date:
Wednesday, October 21, 9:00 am
Symposium:
Wednesday Posters
Topic(s):
Infrared Biological Spectral Analysis
Author(s):
heng chi (presenting) - 1
Institution(s):
1. university of illinois chicago
Abstract:
Spectroscopic determination of conformation in peptides and proteins is ultimately due to utilization of a physical observable dependent on coupling between repeating units in a polymeric chain. Determination of such couplings and their impact on the usable observables such as IR or Raman spectra is thus important for unraveling the spectra-structure relationships that underlie utilization of such techniques. In terms of vibrational spectroscopy, this is equivalent to determination of the off-diagonal force field components between sites in the sequence, which manifest themselves as frequency shifts from the isolated oscillator position (determined from diagonal FF). With isotopic labeling, transitions for specific sites in a peptide sequence can identified, and if the peptide is double labeled, couplings between the sites can be determined.[1,2] Since the vibrational coupling shift is small compared to the bandwidth, the relationship of spectral profiles obtained with various techniques, which give rise to differently weighted intensity patterns, can used to deconvolve the desired parameters. Here theoretical modeling of the expected spectral patterns is an essential part of the analysis. We have prepared a number of short peptides with lengths varying from 8 to 14 residues that are rich in Pro and favor a 31-helical geometry (poly-Pro II like). Since “random coils” are now routinely assigned as having this same conformation, we prepared another series based on Lys oligomers for comparison. Variants of a given sequence were labeled with 13C on the amide C=O in sequential and alternate positions in the center of the sequence, and the couplings were deconvolved using IR and vibrational circular dichroism (VCD) spectra of the amide I transition. In these examples Raman proved to be less useful in yielding differentiable intensity patterns. These couplings are small but vary in a way predicted by our DFT derived FF. They show a different pattern than for alpha-helices, previously published [2], and for 310-helices, currently under study. [1] Rong Huang, Ling Wu, Dan McElheny, Petr Bour, Anjan Roy, Timothy A. Keiderling, J.Phys. Chem. B 113, 5661-5674 (2009); Rong Huang, Vladimir Setnicka, Marcus. A. Etienne, Joohyun Kim, Jan Kubelka, Robert P. Hammer, Timothy A. Keiderling, Journal of the American Chemical Society 129, 13592 -13603 (2007) [2] R. Huang, J. Kubelka, W. Barber-Armstrong, R. A. G. D Silva, S. M. Decatur, and T. A. Keiderling, J. Amer. Chem. Soc., 126, 2346-2354 (2004)
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