CONFORMATIONAL FEATURES OF COMPLEX CARBOHYDRATES IN AQUEOUS SOLUTION AS REVEALED BY HYDROGEN EXCHANGE
The structures of the oligosaccharide prosthetic groups of glycoproteins have become of great interest in recent years largely as a result of the emerging recognition of their role in cell-surface phenomena. Knowledge of the primary structures of glycoprotein carbohydrate chains has grown in concert with increasing interest in their function. In contrast knowledge of possible higher-order structures is quite limited. We have therefore examined the N-linked complex glycopeptide of the serum glycoprotein fetuin, along with several other carbohydrate compounds, using hydrogen exchange techniques. These techniques are sensitive to features of macromolecular conformation and stability. Examined along with the fetuin glycopeptide were small oligosaccharide fragments of hyaluronic acid, the (beta)1-4 linked trimer of N-acetylglucosamine (triNAG), and the monosaccharides N-acetylneuraminic acid and N-acetylglucosamine. The exchange rates of the acetamido hydrogens of the monosaccharides were measured using hydrogen-deuterium techniques while those of the oligosaccharides were measured using hydrogen-tritium techniques. The rates of the small molecule models were then compared with those of the larger molecules. The rates found for the monosaccharide amino sugars and triNAG were essentially identical while those for the hyaluronate fragments and for two of the eight acetamido hydrogens in the glycopeptide were significantly slower. The slowing reflects the limited accessibility of those exchangable hydrogens. The most likely explanation is hydrogen-bonding. In the case of the glycopeptide removal of the three terminal sialic acid residues results in the disappearance of the slowed hydrogens, implicating the role of the sialic acids in the hydrogen-bonded conformation. In the case of hyaluronate the slowing fits well with an intramolecularly hydrogen-bonded structure proposed by others based on more indirect evidence. In both cases the magnitude of the slowing is relatively small suggesting stability constants for the conformations on the order of one kcal/mol or less. These conformations are therefore relatively plastic even though they are present a majority of the time. This concept appears to be in agreement both with the function of molecules of this type as recognition entities and with physical considerations of the nature of the chemical groups present and their disposition in aqueous solution.
OBERHOLTZER, JOHN CARL, "CONFORMATIONAL FEATURES OF COMPLEX CARBOHYDRATES IN AQUEOUS SOLUTION AS REVEALED BY HYDROGEN EXCHANGE" (1982). Dissertations available from ProQuest. AAI8307346.