Studying Collagen Architecture in Solution by Raman Optical Activity Spectroscopy

Raman and Raman optical activity (ROA) spectroscopy provide a unique insight into the three-dimensional structure of biomacromolecules; however, it is often hampered by low sensitivity, low resolution, and the lack of theoretical models. To advance the methodology, we demonstrate that it can discriminate between two collagen proteins, types I and II. The data are interpreted on the basis of molecular modeling correlated with spectra of five synthetic collagen-type peptides serving as simple models. In the peptides, accurate density functional theory (DFT) calculations and correlation of the structure with the spectra are possible, allowing us to determine convenient marker bands linking spectral intensities to the molecular architecture. ROA spectra reflect the polyproline II (PPII) helical conformation of the peptide's main chain and indicate subtle concentration-dependent structural variations in type I collagen. Several vibrational bands originating from proline (Pro), hydroxyproline (Hyp), and the Pro-Hyp-Gly motifs can be related to the collagen triple helix core. ROA spectroscopy thus captures several aspects of collagen's chirality, enables the study of solvent effects and dynamics, and is expected to aid connective tissue studies.