β‐Sheet and associated turn signatures in vibrational Raman optical activity spectra of proteins

Abstract

We have measured the aqueous solution vibrational Raman optical activity (ROA) spectra of concanavalin A, α-chymotrypsin, and β-lactoglobulin, all of which are rich in β-sheet, together with that of the model β-turn peptide L-pro-L-leu-gly-NH₂. Possible ROA signatures of antiparallel β-sheet include a strong sharp positive band at ∼ 1,313 cm” associated with backbone amide III C_αH and NH deformations, and an amide I couplet, negative at low wavenumber and positive at high, centered at ∼1,658 cm⁻¹. Negative ROA bands in the range ∼1,340-1,380 cm⁻¹, which might originate in glycine CH₂ deformations, appear to be characteristic of β-turns. Our results provide further evidence that ROA is a more incisive probe of protein conformation than conventional vibrational spectroscopy, infrared, or Raman, because only those few vibrational coordinates within a given normal mode that sample the skeletal chirality directly contribute to the corresponding ROA band intensity.