Functional characterization of wild-type and mutant human sialin
Functional characterization of wild-type and mutant human sialin
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DOI：
10.1038/sj.emboj.7600464
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发表时间：
2004-11-24
期刊：
影响因子：
11.4
通讯作者：
Gasnier, B
中科院分区：
文献类型：
--
作者：
Morin, P;Sagné, C;Gasnier, B
唾液酸对细胞表面脂质或蛋白质的修饰是许多生物过程所必需的，许多疾病是由唾液酸代谢缺陷引起的。从降解的唾液糖偶联物中分离出来的唾液酸通过一种叫做唾液素的膜转运体从溶酶体中输出，这种转运体在两种等位基因遗传性疾病中存在缺陷：婴儿唾液酸储存病（ISSD）和Salla病。为了开发人唾液素的功能分析，我们通过突变二亮氨酸内化基序将蛋白质重定向到质膜上。表达质乳结构的细胞在酸性pH值下通过一种相当于溶酶体外排的过程积累神经氨酸。该试验用于确定致病突变如何影响运输。有趣的是，虽然两个错义突变和一个与ISSD相关的小的帧内缺失消除了运输，但导致Salla病（R39C）的突变减慢了运输周期，但没有停止，从而解释了为什么后者的疾病不那么严重。由于神经系统症状在萨拉病中占主导地位，我们的研究结果表明唾液酸对神经系统的特定唾液酸依赖过程具有限速作用。
The modification of cell surface lipids or proteins with sialic acid is essential for many biological processes and several diseases are caused by defective sialic acid metabolism. Sialic acids cleaved off from degraded sialoglyco-conjugates are exported from lysosomes by a membrane transporter, named sialin, which is defective in two allelic inherited diseases: infantile sialic acid storage disease (ISSD) and Salla disease. To develop a functional assay of human sialin, we redirected the protein to the plasma membrane by mutating a dileucine-based internalization motif. Cells expressing the plasmalemmal construct accumulated neuraminic acid at acidic pH by a process equivalent to lysosomal efflux. The assay was used to determine how pathogenic mutations affect transport. Interestingly, while two missense mutations and one small, in-frame deletion associated with ISSD abolished transport, the mutation causing Salla disease (R39C) slowed down, but did not stop, the transport cycle, thus explaining why the latter disorder is less severe. Since neurological symptoms predominate in Salla disease, our results suggest that sialin is rate-limiting to specific sialic acid-dependent processes of the nervous system.