Gieselmann V, Schmidt B, von Figura K
Georg-August-Universität, Abteilung Biochemie II, Göttingen, Germany.
J Biol Chem. 1992 Jul 5;267(19):13262-6.
The correct intracellular sorting of lysosomal enzymes such as arylsulfatase A depends on the presence of mannose 6-phosphate residues on high mannose type oligosaccharides. The arylsulfatase A cDNA contains three potential N-glycosylation sites, two of which are utilized. We have mutated one or two of the N-glycosylation sites and analyzed the glycosylation, phosphorylation, and intracellular sorting of the mutant arylsulfatase A polypeptides. The results show that each of the three glycosylation sites (I, II, and III) can be glycosylated, but glycosylation at sites I and II is mutually exclusive. In mutants with one oligosaccharide side chain at positions I, II, or III all side chains can acquire mannose 6-phosphate residues irrespective of their location. This demonstrates spatial flexibility of the phosphotransferase, which specifically recognizes lysosomal enzymes and initiates the addition of mannose 6-phosphate residues on oligosaccharide side chains. However, these mutants have different intracellular sorting efficiencies and seem to use different (mannose 6-phosphate receptor-dependent and -independent) sorting pathways.
溶酶体酶（如芳基硫酸酯酶A）在细胞内的正确分选取决于高甘露糖型寡糖上是否存在甘露糖6-磷酸残基。芳基硫酸酯酶A的cDNA包含三个潜在的N-糖基化位点，其中两个位点被利用。我们对其中一个或两个N-糖基化位点进行了突变，并分析了突变型芳基硫酸酯酶A多肽的糖基化、磷酸化及细胞内分选情况。结果表明，三个糖基化位点（I、II和III）均可发生糖基化，但位点I和II的糖基化相互排斥。在I、II或III位带有一个寡糖侧链的突变体中，所有侧链均可获得甘露糖6-磷酸残基，而不论其位置如何。这证明了磷酸转移酶的空间灵活性，它能特异性识别溶酶体酶并启动在寡糖侧链上添加甘露糖6-磷酸残基的过程。然而，这些突变体具有不同的细胞内分选效率，且似乎使用不同的（依赖和不依赖甘露糖6-磷酸受体的）分选途径。
