Zamze S E, Ashford D A, Wooten E W, Rademacher T W, Dwek R A
Department of Biochemistry, University of Oxford, United Kingdom.
J Biol Chem. 1991 Oct 25;266(30):20244-61.
The complete primary structures of the major Asn-linked oligosaccharides from the type II variant surface glycoproteins (VSGs), MITat 1.2 and MITat 1.7, and the type III VSG, MITat 1.5, were determined using a combination of exo- and endoglycosidase digestions, methylation analysis, acetolysis, and 500 MHz 1H NMR spectroscopy. Each variant contained classical branched oligomannose-type and biantennary complex oligosaccharides, a proportion of the latter substituted with terminal alpha(1-3)-linked galactose residues, the first report of the presence of this epitope in Trypanosoma brucei. In addition both the type II variants contained relatively large amounts of the unusual small oligomannose-type oligosaccharides, Man4GlcNAc2 and Man3GlcNAc2, and a diverse array of novel branched poly-N-acetyllactosamine oligosaccharides, similar but not identical to those from mammalian glycoproteins. These latter structures were also partially substituted with terminal alpha(1-3)-linked galactose residues. Glycosylation in the type II variants showed site specificity in that the poly-N-acetyllactosamine and Man(9-5)GlcNAc2 oligosaccharides were located exclusively at Asn-glycosylation site 1 very close to the C terminus, whereas the Man(4-3)GlcNAc2 and biantennary complex oligosaccharides were located exclusively at site 2. This is the first report of the presence of poly-N-acetyllactosamine oligosaccharides in protozoa.
利用外切糖苷酶和内切糖苷酶消化、甲基化分析、乙酰解和500兆赫氢核磁共振光谱等方法，确定了II型变异表面糖蛋白（VSG）MITat 1.2和MITat 1.7以及III型VSG MITat 1.5中主要天冬酰胺连接寡糖的完整一级结构。每个变异体都含有典型的分支寡甘露糖型和双天线复合寡糖，后者一部分被末端α(1-3)连接的半乳糖残基取代，这是在布氏锥虫中首次报道这种表位的存在。此外，两种II型变异体都含有相对大量不寻常的小寡甘露糖型寡糖，即Man4GlcNAc2和Man3GlcNAc2，以及一系列多样的新型分支聚N-乙酰乳糖胺寡糖，它们与哺乳动物糖蛋白中的寡糖相似但不相同。这些后者的结构也部分被末端α(1-3)连接的半乳糖残基取代。II型变异体中的糖基化表现出位点特异性，即聚N-乙酰乳糖胺和Man(9-5)GlcNAc2寡糖仅位于非常靠近C末端的天冬酰胺糖基化位点1，而Man(4-3)GlcNAc2和双天线复合寡糖仅位于位点2。这是原生动物中存在聚N-乙酰乳糖胺寡糖的首次报道。
