Characteristic Raman Optical Activity Signatures of Protein β‑Sheets

In this study, we compute and analyze
theoretical Raman optical
activity spectra of large model β-sheets in order to identify
reliable signatures for this important secondary structure element.
We first review signatures that have already been proposed to be indicative
of β-sheets. From these signatures, we find that only the couplet
in the amide I region can be regarded as a truly reliable signature.
In addition, we propose a strong negative peak at ∼1350 cm–1 to be another good signature for parallel as well
as antiparallel β-sheets. We study the robustness of these signatures
with respect to perturbations induced by the amino acid side chains,
the overall conformation of the sheet structure, and microsolvation.
It is found that the latter effects can be very well understood and
separated employing the concept of localized modes. Finally, we investigate
whether Raman optical activity is capable of discriminating between
parallel and antiparallel β-sheets. The amide III region turns
out to be most promising for this purpose.