Vibrational circular dichroism in amino acids and peptides. 7. Amide stretching vibrations in polypeptides

Abstract

SynopsisVibrational circular dichroism (VCD) spectra for the principal amide stretching vibrations, amide A (N-H stretch) and amide I (predominantly C=O stretch), are presented and analzyed for a variety of polypeptides dissolved in chloroform, as well as for two examples in DzO. Our results for poly(y-benzyl-L-glutamate) confirm the first and only previous report of VCD in polypeptides carried out by Singh and Keiderling [( ) Biopolymers 20,237-2401. Collectively, our spectra show that, the sense of the hisignate VCD in these two regions depends on the sense of a-helicity and not on the absolute configuration of the constituent amino acids. This conclusion is established by obtaining VCD for the two polypeptides, poly(P-benzyl-L-asparate) and poly(im-henzyl-L-histidine), that form left-handed as opposed to right-handed a-helices. A new amide band having significant VCD intensity owing to its Fermi resonance interaction with the N-H stretching mode has been identified as a weak shoulder on the low-frequency side of the amide A band near 3200 cm-' and is assigned as a combination hand of the amide I and amide I1 vibrations. VCD spectra of polypeptides in DzO solution, although weak, have been successfully measured in the amide I region, where spectra appear to he more complicated due to the presence of solvated and internally hydrogen-honded amide groups.Strong monosignate contributions to the VCD in the amide A and amide I regions for some of the polypeptides indicate coupling of an electronic nature between these two regions and is deduced by an application of the concept of local sum rules of rotational strength. It appears that a detailed understanding of the VCD obtained for polypeptides will not only be diagnostic of secondary structure, but also of more subtle structural and vibrational effects that give rise to local, intrinsic chirality in the amide vibrations.

Vibrational circular dichroism in amino acids and peptides. 10. Fourier transform VCD and Fourier self‐deconvolution of the amide I region of poly(γ‐benzyl‐L‐glutamate)

“…This appears warranted on the basis of the ir spectrum alone, since the amide I absorption band is relatively narrow and intense and gives rise to a VCD spectrum that is, likewise, intense compared with the corresponding spectral features of other a-helical polypeptides. 2 The results of the previous two sections indicate that at least three amide I components are required for the interpretation of the VCD spectra. A similar result using dispersive VCD measurements has recently been obtained by Sen and KeiderlingZ1 for N-deuterated PBLG.…”

Avian pancreatic polypeptide fragments refold to native aPP conformation when combined in solution: A CD and VCD study

“…An antibody specific for the -helical sequence in intact aPP fails to bind the same sequence as a fragment alone. 6 Vibrational circular dichroism (VCD) spectroscopy 7,8 was shown to have some advantages over electronic circular dichroism (ECD) spectroscopy for the study of polypeptide conformation, in particular in being able to distinguish aromatic residue vibrations from carbonyl stretching vibration, whereas the electronic transitions of ECD overlap. [9][10][11][12][13] The chiral sensitivity of VCD is also more effective in demon-strating protein structural changes than is IR spectroscopy.…”

Structural transition during thermal denaturation of collagen in the solution and film states

“…[33][34][35][36][37][38][39][40] Recently, VCD studies from our laboratory have shown that the secondary structures of some proteins in film state are same as those in solution state. 41,42 VCD has been used for both qualitative [43][44][45][46][47][48] and quantitative 34,49-51 secondary structure predictions for proteins. In addition, VCD has the ability to differentiate protein secondary structural features in difficult circumstances, such as those in glycoproteins 52 and ligand binding to proteins.…”