Beck P J, Gething M J, Sambrook J, Lehrman M A
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas 75235.
Somat Cell Mol Genet. 1990 Nov;16(6):539-48. doi: 10.1007/BF01233094.
Dolichol-linked oligosaccharides consisting of two N-acetylglucosamine, nine mannose, and three glucose residues (Glc3Man9GlcNAc2) are transferred to proteins that contain the consensus sequence Asn-X-Ser/Thr. This transfer occurs upon protein import into the lumen of the endoplasmic reticulum. An intermediate in the biosynthesis of the Glc3Man9GlcNAc2 lipid-linked oligosaccharide contains two GlcNAc and five mannose residues. This intermediate serves as a substrate for further mannosylation and glucosylation before transfer to protein. The addition of the sixth mannose residue to this intermediate requires the enzyme mannosyltransferase VI and the mannose donor, mannose-P-dolichol. Several different CHO cell line mutants that fail to efficiently catalyze this transfer have been described. In this report, we examine seven independent mutant cell lines with various biochemical phenotypes and demonstrate that all can be assigned to one of three genetic complementation groups. One mutation affects mannose-P-dolichol biosynthesis (Lec15), three affect dolichol phosphate biosynthesis (Lec9), and three appear to affect the functional orientation of enzyme substrates (PIR).
由两个N - 乙酰葡糖胺、九个甘露糖和三个葡萄糖残基组成的多萜醇连接的寡糖（Glc3Man9GlcNAc2）被转移到含有共有序列Asn - X - Ser/Thr的蛋白质上。这种转移发生在蛋白质导入内质网腔时。Glc3Man9GlcNAc2脂质连接寡糖生物合成的一个中间体含有两个N - 乙酰葡糖胺和五个甘露糖残基。这个中间体在转移到蛋白质之前作为进一步甘露糖基化和糖基化的底物。向这个中间体添加第六个甘露糖残基需要甘露糖基转移酶VI和甘露糖供体甘露糖 - P - 多萜醇。已经描述了几种不能有效催化这种转移的不同CHO细胞系突变体。在本报告中，我们研究了七个具有不同生化表型的独立突变细胞系，并证明它们都可以归为三个遗传互补组之一。一个突变影响甘露糖 - P - 多萜醇的生物合成（Lec15），三个影响磷酸多萜醇的生物合成（Lec9），三个似乎影响酶底物的功能取向（PIR）。
