Biomacromolecular affinity: interactions between lysozyme and regioselectively sulfated chitosan.

It is well known that the sulfate groups on different positions in polysaccharides play important roles in protein adsorption. However, the interactions between sulfated chitosans and lysozyme have not been clearly elucidated. In this study, the regioselectively sulfated chitosans, 6-O-sulfated chitosan (C6S), 2-N-6-O-sulfated chitosan (C26S) and 3,6-O-sulfated chitosan (C36S), were chosen to investigate the possible mechanisms determining the interaction between lysozyme and the sulfated chitosans. It has been found that the selectively sulfated products of chitosan (CS), C6S, C26S and C36S all exhibit lysozyme binding activity. However, the maximum binding ratios of lysozyme/polysaccharide are significantly different for C6S, C26S and C36S. In addition, though C6S possesses the lowest sulfur content among the three sulfated chitosans, it exhibits the highest binding activity with lysozyme. Furthermore, in the protein mixtures, C6S shows the highest selective binding activity with lysozyme among the three sulfated chitosans in the presence of gamma-globulin and bovine serum albumin (BSA). The results indicate that 6-O-sulfate groups may be responsible for the high affinity and specific interaction of sulfated chitosan with lysozyme, while 2-O-sulfate and 3-O-sulfate groups are unfavorable to this interaction.