Interactions between chondroitin‐6‐sulfate and poly‐L‐lysine in aqueous solution: Circular dichroism studies

Abstract

AbstractThe interactions between chondroitin‐6‐sulfate (chondroitin sulfate C) and poly‐L‐lysine have been studied as models for investigation of possible complex formation between fibrous proteins and mucopolysaccharides. Results obtained using circular dichroism spectroscopy show that poly‐L‐lysine adopts the α‐helical conformation in dilute aqueous salt solution at pH 7 when mixed with chondroitin‐6‐sulfate, rather than the “charged‐coil” observed in the absence of this mucopolysaccharide. This conformation‐directing interaction is at a maximum when the ratio of lysine to disaccharide residues is 1 : 1. Changes in the CD spectrum of a 1 : 1 mixture following increase in the salt concentration, or addition of non‐polar solvents, indicate that the interaction is ionic in nature. No such effects are observed for non‐sulfated mucopolysaccharides mixed with poly‐L‐lysine, suggesting that, for chondroitin‐6‐sulfate, it is the sulfate groups rather than the carboxyls which interact with the amine groups of the polypeptide.Elevation of the temperature leads to disruption of the interactions between the polypeptide and polysaccharide species. A sharp melting transition occurs at 47.0 ± 1.0°C, when the poly‐L‐lysine reverts to the “charged‐coil” conformation. The sharp transition suggests that regular ionic bonds are formed between the polypeptide and polysaccharide. These results suggest that a conformation‐directing interaction may occur between sulfated mucopolysaccharides and the polar regions of collagen and other fibrous proteins.