Gomez L, Chrispeels M J
Department of Biology, University of California at San Diego, La Jolla 92093-0116.
Proc Natl Acad Sci U S A. 1994 Mar 1;91(5):1829-33. doi: 10.1073/pnas.91.5.1829.
N-Acetylglucosaminyltransferase I (EC 2.4.1.101) initiates the conversion of high-mannose asparagine-linked glycans to complex asparagine-linked glycans in plant as well as in animal cells. This Golgi enzyme is missing in the cgl mutant of Arabidopsis thaliana, and the mutant cells are unable to synthesize complex glycans. Transformation of cells from the mutant plants with the cDNA encoding human N-acetylglucosaminyltransferase I restores the wild-type phenotype of the plant cells. Fractionation of the subcellular organelles on isopycnic sucrose gradients shows that the human enzyme in the complemented cells bands at the same density, 1.14 g/cm3, typical of Golgi cisternae, as the enzyme in the wild-type plant cells. These results demonstrate that complementation results from the presence of the human enzyme in the plant Golgi apparatus, where it is functionally integrated into the biosynthetic machinery of the plant cell. In addition, given the evolutionary distance between plants and mammals and the great diversity of glycoproteins that are modified in each, there is probably no specific recognition between this Golgi enzyme and the polypeptide domains of the proteins it modifies.
N-乙酰葡糖胺基转移酶I（EC 2.4.1.101）在植物和动物细胞中启动了高甘露糖型天冬酰胺连接聚糖向复杂型天冬酰胺连接聚糖的转化。拟南芥的cgl突变体中缺少这种高尔基体酶，且突变体细胞无法合成复杂聚糖。用编码人N-乙酰葡糖胺基转移酶I的cDNA转化突变体植物的细胞，可恢复植物细胞的野生型表型。在等密度蔗糖梯度上对亚细胞器进行分级分离表明，互补细胞中的人酶与野生型植物细胞中的酶一样，在1.14 g/cm3这一典型的高尔基体潴泡密度处形成条带。这些结果表明，互补作用源于人酶存在于植物高尔基体中，且在其中它功能性地整合到了植物细胞的生物合成机制中。此外，鉴于植物和哺乳动物之间的进化距离以及各自修饰的糖蛋白的巨大多样性，这种高尔基体酶与其修饰的蛋白质的多肽结构域之间可能不存在特异性识别。
