Molecular Structure and Function Program, Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada, M5G 1X8,
Glycoconj J. 2014 Jan;31(1):1-5. doi: 10.1007/s10719-013-9507-5. Epub 2013 Nov 2.
The synthesis of complex asparagine-linked glycans (N-glycans) involves a multi-step process that starts with a five mannose N-glycan structure: [Manα1-6(Manα1-3)Manα1-6][Manα1-3]-R where R = Manβ1-4GlcNAcβ1-4GlcNAcβ1-Asn-protein. N-acetylglucosaminyltransferase I (GlcNAc-TI) first catalyzes addition of GlcNAc in β1-2 linkage to the Manα1-3-R terminus of the five-mannose structure. Mannosidase II then removes two Man residues exposing the Manα1-6 terminus that serves as a substrate for GlcNAc-T II and addition of a second GlcNAcβ1-2 residue. The resulting structure is the complex N-glycan: GlcNAcβ1-2Manα1-6(GlcNAcβ1-2Manα1-3)-R. This structure is the precursor to a large assortment of branched complex N-glycans involving four more N-acetylglucosaminyltransferases. This short review describes the experiments (done in the early 1970s) that led to the discovery of GlcNAc-TI and II.
复杂天冬酰胺连接聚糖（N-聚糖）的合成涉及一个多步骤的过程，从五甘露糖 N-聚糖结构开始：[Manα1-6(Manα1-3)Manα1-6][Manα1-3]-R，其中 R=Manβ1-4GlcNAcβ1-4GlcNAcβ1-Asn-蛋白。N-乙酰氨基葡萄糖基转移酶 I（GlcNAc-TI）首先催化在 Manα1-3-R 末端的五甘露糖结构中添加 GlcNAc，以β1-2 键连接。然后甘露糖苷酶 II 去除两个 Man 残基，暴露出作为 GlcNAc-T II 和第二个 GlcNAcβ1-2 残基添加的底物的 Manα1-6 末端。所得结构是复杂的 N-聚糖：GlcNAcβ1-2Manα1-6（GlcNAcβ1-2Manα1-3）-R。该结构是涉及另外四个 N-乙酰氨基葡萄糖基转移酶的大量分支复杂 N-聚糖的前体。这篇简短的综述描述了导致发现 GlcNAc-TI 和 II 的实验（在 20 世纪 70 年代早期进行）。
