Kitagawa H, Tanaka Y, Tsuchida K, Goto F, Ogawa T, Lidholt K, Lindahl U, Sugahara K
Department of Biochemistry, Kobe Pharmaceutical University, Japan.
J Biol Chem. 1995 Sep 22;270(38):22190-5. doi: 10.1074/jbc.270.38.22190.
During the course of a study of elucidate the role of modification of the common polysaccharide-protein linkage structure, GlcA beta 1-3Gal beta 1-3Gal beta 1-4Xyl beta 1-O-Ser, in biosynthetic sorting mechanisms of the different sulfated glycosaminoglycan chains, a novel N-acetylgalactosamine (GalNAc) transferase was discovered in fetal bovine serum. The enzyme catalyzed the transfer of [3H]GalNAc from UDP-[3H]GalNAc to linkage tetrasaccharide and hexasaccharide serines synthesized chemically and to various regular oligosaccharides containing terminal D-glucuronic acid (GlcA), which were prepared from chondroitin and chondroitin sulfate using testicular hyaluronidase digestion. The labeled products obtained with the linkage tetra- and hexasaccharide serines and with the tetrasaccharide (GlcA beta 1-3GalNAc)2 were resistant to digestion with chondroitinase AC-II and beta-N-acetylhexosaminidase but sensitive to alpha-N-acetylgalactosaminidase digestion, indicating that the enzyme is an alpha-N-acetylgalactosaminyltransferase. This finding is in contrast to that of Rohrmann et al. (Rohrmann, K., Niemann, R., and Buddecke, E. (1985) Eur. J. Biochem., 148, 463-469), who reported that a corresponding product was susceptible to digestion with beta-N-acetylhexosaminidase. The presence of a sulfate group at C4 of the penultimate GalNAc or Gal units markedly inhibited the transfer of GalNAc to the terminal GlcA, while a sulfate group at C6 of the GalNAc had little effect on the transfer. Moreover, a slight but significant transfer of [3H]GalNAc was observed to an oligosaccharide containing terminal 2-O-sulfated GlcA as acceptor, whereas no incorporation was detected into oligosaccharides containing terminal unsaturated or 3-O-sulfated GlcA units. These results suggest that this novel serum enzyme is a UDP-GalNAc:chondro-oligosaccharide alpha 1-3- or 1-4-N-acetylgalactosaminyltransferase. The possibility of involvement of this enzyme in glycosaminoglycan biosynthesis is discussed.
在一项旨在阐明常见多糖 - 蛋白质连接结构(GlcAβ1 - 3Galβ1 - 3Galβ1 - 4Xylβ1 - O - Ser)在不同硫酸化糖胺聚糖链生物合成分选机制中的作用的研究过程中,在胎牛血清中发现了一种新型的N - 乙酰半乳糖胺(GalNAc)转移酶。该酶催化将[³H]GalNAc从UDP - [³H]GalNAc转移至化学合成的连接四糖和六糖丝氨酸以及各种含有末端D - 葡萄糖醛酸(GlcA)的规则寡糖,这些寡糖是使用睾丸透明质酸酶消化硫酸软骨素和硫酸软骨素制备得到的。用连接四糖和六糖丝氨酸以及四糖(GlcAβ1 - 3GalNAc)₂获得的标记产物对软骨素酶AC - II和β - N - 乙酰己糖胺酶的消化具有抗性,但对α - N - 乙酰半乳糖胺酶消化敏感,表明该酶是一种α - N - 乙酰半乳糖胺基转移酶。这一发现与Rohrmann等人(Rohrmann, K., Niemann, R., and Buddecke, E. (1985) Eur. J. Biochem., 148, 463 - 469)的发现相反,他们报道相应产物对β - N - 乙酰己糖胺酶的消化敏感。倒数第二个GalNAc或Gal单元的C4位存在硫酸基团显著抑制了GalNAc向末端GlcA的转移,而GalNAc的C6位硫酸基团对转移影响很小。此外,观察到[³H]GalNAc有轻微但显著的转移至含有末端2 - O - 硫酸化GlcA作为受体的寡糖,而未检测到其掺入含有末端不饱和或3 - O - 硫酸化GlcA单元的寡糖中。这些结果表明这种新型血清酶是一种UDP - GalNAc:软骨寡糖α1 - 3 - 或1 - 4 - N - 乙酰半乳糖胺基转移酶。讨论了该酶参与糖胺聚糖生物合成的可能性。