Effects of sulfation and the environment on the structure of chondroitin sulfate studied via Raman optical activity.

Glycosaminoglycans are linear carbohydrate polymers with essential roles in many biological processes. Chondroitin sulfate (CS) is one of them, omnipresent in living organisms as an important structural component of cartilage. It provides much of its resistance to compression. Despite its biological importance, little is still known about the relation of the CS structure to chemical composition and interaction with the environment. We therefore measured Raman and Raman optical activity (ROA) spectra of five CS samples of different biological origin and variously sulfated CS building blocks (GlcA, GalNAc, and basic disaccharide units) in a wide frequency range between 200 cm-1 and 1800 cm-1 and analyzed them with respect to specific structure marker bands. We show that ROA spectroscopy is sensitive to the conformational stability and rigidity of pyranose rings of saccharides, the orientation of sugar hydroxyl groups and the secondary structure of the CS's backbone. The CS secondary structure has been found to be quite stable, with a minor variation as a reaction to physicochemical parameters (concentration, pH, temperature, and the presence of cations). Larger changes were observed under chemical changes (sulfation) of the CS chain. ROA spectroscopy thus exhibited useful potential to study the structure of similar biopolymers.