Natowicz M, Hallett D W, Frier C, Chi M, Schlesinger P H, Baenziger J U
J Cell Biol. 1983 Mar;96(3):915-9. doi: 10.1083/jcb.96.3.915.
The intracellular transport of newly synthesized lysosomal hydrolases to lysosomes requires the presence of one or more phosphorylated high mannose-type oligosaccharides per enzyme. A receptor that mediates mannose-6-PO4-specific uptake of lysosomal enzymes is expressed on the surface of fibroblasts and presumably accounts for the intracellular transport of newly synthesized enzymes to the lysosome. In this study, we examined the internalization of lysosomal enzyme-derived phosphorylated oligosaccharides by cultured human fibroblasts. Oligosaccharides of known specific activity bearing a single phosphate in monoester linkage were internalized with Kuptake of 3.2 X 10(-7) M, whereas oligosaccharides bearing two phosphates in monoester linkage were internalized with a Kuptake of 3.9 X 10(-8) M. Thus, phosphorylated high mannose-type oligosaccharides appear to be the minimal structure required for recognition and uptake by the fibroblast receptor. The finding that the Kuptake for monophosphorylated oligosaccharides is 100-fold less than the reported Ki for mannose-6-phosphate indicates that the fibroblast phosphomannosyl receptor contains a binding site that recognizes features of the oligosaccharide in addition to mannose-6-phosphate.
新合成的溶酶体水解酶向溶酶体的细胞内运输要求每种酶都存在一个或多个磷酸化的高甘露糖型寡糖。一种介导溶酶体酶的甘露糖-6-磷酸特异性摄取的受体在成纤维细胞表面表达，大概负责新合成的酶向溶酶体的细胞内运输。在本研究中，我们检测了培养的人成纤维细胞对溶酶体酶衍生的磷酸化寡糖的内化作用。具有单磷酸单酯键且比活已知的寡糖以内化常数3.2×10⁻⁷M被内化，而具有双磷酸单酯键的寡糖以内化常数3.9×10⁻⁸M被内化。因此，磷酸化的高甘露糖型寡糖似乎是成纤维细胞受体识别和摄取所需的最小结构。单磷酸化寡糖的内化常数比报道的甘露糖-6-磷酸的抑制常数低100倍，这一发现表明成纤维细胞磷酸甘露糖基受体除了甘露糖-6-磷酸外还含有一个识别寡糖特征的结合位点。
