Giuntoli R L, Stoykova L I, Gillies D R, Glick M C
Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia.
Eur J Biochem. 1994 Oct 1;225(1):159-66. doi: 10.1111/j.1432-1033.1994.00159.x.
Terminal glycosylation may be a mechanism to control the function of specific biologically active glycoproteins. The biosynthesis of terminal sialyl and fucosyl residues on certain glycoproteins has been linked to the expression of the respective glycosyltransferase. In contrast, a human erythroleukemia cell line, HEL, contained a highly active GDP-L-Fuc: Gal(beta 1-4)GlcNAc-R (Fuc to GlcNAc) alpha-1,3-fucosyltransferase (alpha-1,3-fucosyltransferase) but no detectable alpha-1,3-linked fucosyl residues on the glycoproteins. The alpha-1,3-fucosyltransferase gave apparent Km values for Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc beta-O-benzyl, Gal(beta 1-4)GlcNAc and GDP-fucose of 0.04, 0.68 and 0.12 mM, respectively. The lack of detectable fucosyl residues in alpha-1,3-linkage to GlcNAc on the [3H]fucose-labeled glycoproteins was shown with the use of almond alpha-1,3/4-fucosidase and internal controls to verify that the enzyme was active. Using Western-blot analysis, HEL cell glycoproteins reacted with blood group H type-2 antibody, confirming the presence of Fuc(alpha 1-2)Gal(beta 1-4)GlcNAc as reported by others and the presence of the preferred substrate for the enzyme. It is proposed that controls for terminal glycosylation in addition to glycosyltransferase expression are operative in HEL cells and that they are part of a multi-regulated process controlling terminal modifications of glycoproteins.
末端糖基化可能是一种控制特定生物活性糖蛋白功能的机制。某些糖蛋白上末端唾液酸和岩藻糖基残基的生物合成与各自糖基转移酶的表达有关。相比之下，人红白血病细胞系HEL含有一种高活性的GDP-L-岩藻糖：Gal(β1-4)GlcNAc-R（岩藻糖到GlcNAc）α-1,3-岩藻糖基转移酶（α-1,3-岩藻糖基转移酶），但其糖蛋白上未检测到α-1,3-连接的岩藻糖基残基。α-1,3-岩藻糖基转移酶对Fuc(α1-2)Gal(β1-4)GlcNAcβ-O-苄基、Gal(β1-4)GlcNAc和GDP-岩藻糖的表观Km值分别为0.04、0.68和0.12 mM。通过使用杏仁α-1,3/4-岩藻糖苷酶和内部对照来验证酶的活性，结果表明在[3H]岩藻糖标记的糖蛋白上缺乏与GlcNAc呈α-1,3-连接的可检测到的岩藻糖基残基。使用蛋白质印迹分析，HEL细胞糖蛋白与血型H2型抗体发生反应，证实了其他人报道的Fuc(α1-2)Gal(β1-4)GlcNAc的存在以及该酶的首选底物的存在。有人提出，除了糖基转移酶表达外，HEL细胞中还存在末端糖基化的调控机制，并且它们是控制糖蛋白末端修饰的多调控过程的一部分。
