Molecular basis of lysosomal storage disease and the possibility of a new therapeutic approach

(1)人α-半乳糖苷的组织特异性翻译后修饰在人α-半乳糖苷酶（α-Gal）转基因小鼠中检测异质基因表达和翻译后糖基化。小鼠的心脏和肝脏中表达了大量的转录本和高α-Gal活性。其基因产物在心脏和肾脏中对内糖苷酶H消化敏感，而在脾脏和肝脏中则有很大的抗性。糖肽酶F处理证实该酶的肽段具有相同的分子质量。我们得出结论，基因产物的异质分子质量是由小鼠组织中不同程度的翻译后糖基化引起的。(2) Morquio B病患者突变型β-半乳糖苷酶底物特异性改变β-半乳糖苷酶缺乏症是由酸性β-半乳糖苷酶（β-Gal）缺乏引起的溶酶体贮积性疾病，有两种不同的临床表型，gm1神经节脂质沉积症和Morquio B病。前者有中枢神经系统病变，而后者有骨骼病变，没有中枢神经系统病变。为了阐明这两种疾病之间临床差异的分子证据，我们使用人工底物类似物研究了源自gm1神经节脂质病和Morquio B病患者的突变β-Gal的底物特异性。与gm1神经节苷类似物Galβ1-3GalNAc相比，Morquio B病突变体β-Gal （W237L/W237L, Y83H/R482C）对硫酸角蛋白类似物Galβl-4Glc NAc的亲和力相对较低，但gm1神经节苷病突变体β-Gal （R201C/R201C, 151T/151T）与正常β-Gal的亲和力无明显差异。此外，Morquio B突变体对类似物（Galβ1-4GlcNAc/Galβ1-3GalNAc）的水解率显著降低，而gm1神经节脂质病突变体的水解率与正常的β-Gal相似。我们得出结论，gm1神经节脂质沉积症和Moquio B病之间不同的临床表型是由Morquio B病患者独特的基因突变导致突变P-Gal底物特异性改变引起的。少

(1) Tissue-specific posttranslational modification of human α-galactosidaseHeterogeneous gene expression and posttranslational glycosylation were examined in human α-galactosidase (α-Gal) transgenic mouse. The heart and liver of the mouse expressed a high amount of transcript as well as high α-Gal activity. Its gene products in the heart and kidney were sensitive to endoglycosidase H digestion, but those in the spleen and liver were largely resistant. Glycopeptidase F treatment confirmed an identical molecular mass for the peptide moiety of the enzyme. We conclude that heterogeneous molecular mass of the gene products is caused by different degree of posttranslational glycosylation in murine tissues.(2) Altered substrate specificity of mutant β-galactosidase in patients with Morquio B diseaseβ-Galactosidodosis is a lysosomal storage disease caused by a deficiency of acid β-galactosidase (β-Gal) consisting of two different clinical phenotypes, GM1-gangliosidosis and Morquio B disease. T … More he former has central nervous system lesions, whereas the latter has skeletal lesions with no central nervous system lesions. To clarify the molecular evidence to account for clinical difference between both diseases, we investigated substrate specificity of mutant β-Gal derived from patients with GM1-gangliosidosis and Morquio B disease using artificial substrate analogs. Mutant β-Gal (W237L/W237L, Y83H/R482C) from Morquio B disease exhibited relatively low affinity to Galβl-4Glc NAc , an analog of keratan sulfate, as compared with Galβ1-3GalNAc, an analog of GM1-gangliosid, but there was not such difference in both normal β-Gal and mutant β-Gal (R201C/R201C, 151T/151T) from GM1-gangliosidosis. Furthermore, Morquio B mutants showed considerable decrease in hydrolysis ratio for the analogs (Galβ1-4GlcNAc/Galβ1-3GalNAc), yet GM1-gangliosidosis mutants had similar hydrolysis ratio to normal β-Gal. We conclude that distinct clinical phenotypes between GM1-gangliosidosis and Moquio B disease are caused by altered substrate specificity of mutant P-Gal resulting from unique gene mutations in patients with Morquio B disease. Less