Secondary structures in hyaluronan solutions: chemical and biological implications

Hyaluronan behaves as an unusually stiff polymer in solution. Periodate oxidation of the hexuronic acid moiety is severely hindered, as is that of chondroitin 4-sulphates and 6-sulphates. On the basis of X-ray and computer studies a secondary structure was proposed which accounted for the known facts. NMR data obtained subsequently in dimethyl sulphoxide were completely compatible with these proposals. Results obtained in H2O suggested that the acetamido group could not be oriented in aqueous solution as it was in dimethyl sulphoxide solution. There is strong evidence that an H2O bridge between the acetamido and carboxylate groups is involved in the secondary structure in H2O. It is suggested that conversion of one structure (stable in the absence of H2O) to the other (in aqueous solution) might occur during biosynthesis, as part of the driving force that results in shedding from the H2O-poor environment of the membrane. The hydrogen-bonded secondary structures show quite large arrays of contiguous CH groups, giving a hydrophobic character to some parts of the polymer, which might be significant in self-association and for interactions with membranes.