Vladutiu G D
Biochim Biophys Acta. 1983 Nov 8;760(3):363-70. doi: 10.1016/0304-4165(83)90374-4.
Cultured fibroblasts from patients with the lysosomal storage disease, mucolipidosis II, produce complex glycosylated lysosomal enzymes which are preferentially excreted presumably due to the absence of specific phosphomannosyl recognition residues needed for intracellular retention. Complex glycosylated hydrolases are also produced by fibroblasts from patients with mucolipidosis I but an abnormal excretion is not apparent in this disorder. Intra- and extracellular distribution, lectin binding, and specific endocytosis were criteria used to compared the properties of intra- and extracellular beta-hexosaminidase derived from mucolipidosis I and normal fibroblast cultures. Mucolipidosis I fibroblasts did not hyperexcrete beta-hexosaminidase when maintained in serum-free medium. Using the specificity of ricin binding to terminal galactosyl residues, the most galactosylated forms of the enzyme derived from mucolipidosis I cell extracts and culture fluids were found in the mucolipidosis I cell extracts (50% of total enzyme). Mucolipidosis I-excreted beta-hexosaminidase which was eluted from ricin-120-Sepharose, was a high-uptake form in endocytosis experiments while unbound enzyme was a low-uptake form. These data suggest that beta-hexosaminidase molecules contained phosphomannosyl residues necessary for receptor-mediated endocytosis as well as galactosyl residues on the same molecule. The co-existence of complex chains with high-mannose chains did not interfere with the phosphomannose-mediated endocytosis of beta-hexosaminidase nor with the retention of endogenous enzyme. We can speculate that since complex oligosaccharide chains in the mucolipidosis I cellular enzyme persist due to a sialidase deficiency, more extensive sialylation of cellular enzyme in normal fibroblasts probably occurs at some point during post-translational processing. However, the presence of sialidase in normal cells initiates complex chain trimming in the lysosomes resulting in a less glycosylated end product.
来自溶酶体贮积病粘脂贮积症II患者的培养成纤维细胞产生复杂糖基化的溶酶体酶，这些酶可能由于缺乏细胞内滞留所需的特定磷酸甘露糖识别残基而优先分泌。粘脂贮积症I患者的成纤维细胞也产生复杂糖基化的水解酶，但在这种疾病中未观察到异常排泄。细胞内和细胞外分布、凝集素结合和特异性内吞作用是用于比较粘脂贮积症I和成纤维细胞正常培养物中细胞内和细胞外β-己糖胺酶特性的标准。粘脂贮积症I成纤维细胞在无血清培养基中培养时不会过度分泌β-己糖胺酶。利用蓖麻毒素与末端半乳糖基残基结合的特异性，发现粘脂贮积症I细胞提取物中该酶的半乳糖基化形式最多（占总酶的50%），这些形式来自粘脂贮积症I细胞提取物和培养液。从蓖麻毒素-120-琼脂糖凝胶上洗脱的粘脂贮积症I分泌的β-己糖胺酶在胞吞实验中是高摄取形式，而未结合的酶是低摄取形式。这些数据表明，β-己糖胺酶分子含有受体介导的胞吞作用所需的磷酸甘露糖残基以及同一分子上的半乳糖基残基。复杂链与高甘露糖链的共存并不干扰β-己糖胺酶的磷酸甘露糖介导的胞吞作用，也不干扰内源性酶的滞留。我们可以推测，由于粘脂贮积症I细胞酶中的复杂寡糖链因唾液酸酶缺乏而持续存在，正常成纤维细胞中细胞酶的唾液酸化可能在翻译后加工的某个阶段更广泛地发生。然而，正常细胞中唾液酸酶的存在会启动溶酶体中复杂链的修剪，导致糖基化程度较低的终产物。
