Hara Y, Nishimoto J, Suzuki K
Department of Neurology, University of North Carolina School of Medicine, Chapel Hill 27599.
Biochim Biophys Acta. 1994 Jan 18;1217(1):49-53.
We observed earlier that there are 5 nucleotide polymorphisms in the protein coding sequence of the acid beta-galactosidase gene between the C57BL/6J and DBA/2J strains of mice. Two of them result in amino acid substitutions. Consequences of the difference in the primary amino acid sequence were studied by introducing the two DBA polymorphisms into the C57BL cDNA, individually and in combination, by oligonucleotide-directed mutagenesis and expressing the resultant cDNAs in the COS-1 cell expression system. Introduction of one polymorphism, Asn517-->Asp into the C57BL cDNA, did not alter the acid beta-galactosidase activity in the transfected COS-1 cells, while introduction of Gly539-->Arg completely abolished the catalytic activity. When both polymorphisms were introduced together, as in the DBA mice, however, the acid beta-galactosidase activity was restored to that of the C57BL level. Thus, Asn517-->Asp appears to counteract the activity-abolishing effect of Gly539-->Arg, although it does not by itself raise the catalytic activity. All four types of cDNA generated similarly large amounts of stable mRNA in COS-1 cells. These results do not explain the significantly low acid beta-galactosidase activity in tissues of DBA mice, described earlier and also confirmed in this study.
我们之前观察到，在C57BL/6J和DBA/2J品系小鼠的酸性β-半乳糖苷酶基因的蛋白质编码序列中存在5个核苷酸多态性。其中两个导致氨基酸替换。通过寡核苷酸定向诱变将两个DBA多态性分别或组合引入C57BL cDNA中，并在COS-1细胞表达系统中表达所得cDNA，研究了一级氨基酸序列差异的后果。将一个多态性Asn517→Asp引入C57BL cDNA中，并未改变转染的COS-1细胞中的酸性β-半乳糖苷酶活性，而引入Gly539→Arg则完全消除了催化活性。然而，当像在DBA小鼠中那样将两种多态性一起引入时，酸性β-半乳糖苷酶活性恢复到C57BL水平。因此，Asn517→Asp似乎抵消了Gly539→Arg的活性消除作用，尽管它本身不会提高催化活性。所有四种类型的cDNA在COS-1细胞中产生的稳定mRNA量相似。这些结果无法解释先前描述并在本研究中得到证实的DBA小鼠组织中酸性β-半乳糖苷酶活性显著较低的现象。
