Vibrational circular dichroism of polypeptides and proteins

Abstract

Vibrational circular dichroism spectra of poly-L-tyrosine, poly-L-phenylalanine, myoglobin and fl-lactoglobulin were measured in solution for the amide I region. These measurements are shown to be consistent with previous determinations of the secondary structures of these species.

Structure of Condensed Phase Peptides: Insights from Vibrational Circular Dichroism and Raman Optical Activity Techniques

“…190,288,309 By contrast with ECD analyses, highly aromatic peptides were shown to give straightforwardly interpretable VCD, with no side chain interference, since the aromatic vibrations were resolved from the amide bands. 299,300,302,304 The observed patterns were directly relatable to those of aliphatic side-chain peptides having the same helical secondary structure.…”

“…This polypeptide has such a long persistence length that liquid crystals form in some solvents at higher concentrations resulting in very strong VCD intensities . Subsequent studies with other peptides and proteins showed that these initially observed frequency and VCD sign patterns were diagnostic of the secondary structure, even for peptides in H 2 O solution, but the amide II and III bands are broader than the amide I and provide less distinct conformational evidence. − Nafie and co-workers confirmed that α-helical amide I VCD results were consistent for several peptides and also obtained spectra of the opposite sign pattern for peptides thought to form left-handed helices. ,, These amide I patterns, whose sign patterns flip for peptides made with d -amino acids, , proved, after many studies of a variety of helical peptides and proteins, to be uniquely characteristic of the helicity. ,,− Unique deuteration effects were noted for α-helices, in which the amide I′ (N-D) VCD gained a new lower frequency negative feature resulting in both a weaker and narrower (central) positive component. ,, By contrast with ECD analyses, highly aromatic peptides were shown to give straightforwardly interpretable VCD, with no side chain interference, since the aromatic vibrations were resolved from the amide bands. ,,, The observed patterns were directly relatable to those of aliphatic side-chain peptides having the same helical secondary structure.…”