ミルクオリゴ糖の糖修飾基情報から生理活性素材を創る!―糖質化学分野における新マテリアルサイエンスの創成―

抄録

It is well known that the carbohydrate moieties of glycoproteins or glycolipids, which exist on mammalian cell surfaces, are modified by sulfate or phosphate, etc, in a few cases. These modifiers are recognised as possible receptors in intercellular communications. On the other hand, mammalian milk or colostrum contains many kinds of free oligosaccharides other than lactose in common. These oligosaccharides are also suggested to have biological roles such as inhibition of the adhesion of pathogenic microorganisms to the intestinal tract of infant or brain development - stimulation in infants. Recently, a few milk oligosaccharides have also been shown to be modified and the biological significance of these saccharides are assumed as follows: 1) Sialyllactose lactone: Some proportion of Neu5Gc(α2-3)Gal(β1-4)Glc was found to occur as free lactones between the carboxyl group of Neu5Gc and OH of Gal or Neu5Gc itself (sialyllactose lactone) in ovine colostrum. The sialyl oligosaccharides in milk or colostrum may attach to bacterial toxin and viruses, such as influenza virus in the intestine, thus protecting the infant. The lactone can be assumed to be resistant to virus sialidase. When the sialic acid is liberated from sialyl oligosaccharides by virus sialidase, they would lose their protective effect but the lactone should retain this effect because of its resistance to the action of virus sialidase. 2) 4-O-acetylated sialyllactose: Neu5Ac(α2-3)Gal(β1-4) Glc, whose Neu5Ac was O -acetylated at OH-4, was identified in the milk of echidna, one of the monotremes. Although this saccharide was assumed to be a possible inhibitor for the adhesion of viruses or bacteria whose receptors are O -acetylated Neu5Ac, the exact function of this saccharide is still unknown. 3) sulfated oligosaccharides: Gal(β1-4)Glc-6'-O-sulphate (lactose 6'-O -sulfate) and Neu5Ac(α2-3)Gal(β1-4)Glc-6'-O-sulfate (N-acetylneuraminyllactose 6'-O-sulfate) were identified in rat milk, whereas Gal(β1-4)Glc-3'-O-sulfate (lactose 3'-O-sulfate) was found in dog milk. The presence of N-acetylneuraminyllactose 6'-O -sulfate is suggested in human milk, too, and, in addition, this milk contained oligosaccharides whose GlcNAc residues were replaced by sulfate at OH-6 position. These compounds may permit the simultaneous delivery of two essential nutrients, sulfate and calcium, in early life, avoiding the precipitation of insoluble calcium sulfate in milk. 4) phosphorylated oligosaccharides: Bovine or mare colostrum contained phosphorylated oligosaccha-rides including Neu5Ac(α2-6)Gal(β1-4)GlcNAc-a1-phosphate (cow), Neu5Ac(α2-6)Gal(β1-4)GlcNAc-6-phosphate (cow) and Gal(β1-4)GlcNAc-α1-phophate (horse). These oligosaccharides may also permit the simultaneous delivery of phosphate and calcium, avoiding the precipitation of calcium phosphate. The existence of these modified oligosaccharides in milk may offer valuable in-formation for manufacturing bio-functional materials in the food industry.