Two naturally occurring alpha2,6-sialyltransferase forms with a single amino acid change in the catalytic domain differ in their catalytic activity and proteolytic processing.
Two naturally occurring alpha2,6-sialyltransferase forms with a single amino acid change in the catalytic domain differ in their catalytic activity and proteolytic processing.
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催化结构域中具有单个氨基酸变化的两种天然存在的 α2,6-唾液酸转移酶形式在催化活性和蛋白水解加工方面有所不同。
DOI：
10.1074/jbc.272.1.672
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发表时间：
1997
期刊：
影响因子：
--
通讯作者：
Colley,KJ
中科院分区：
文献类型：
--
作者：
Ma,J;Qian,R;Rausa3rd,FM;Colley,KJ
α 2，6-唾液酸转移酶（ST）是一种高尔基体糖基转移酶，可将唾液酸残基添加到糖蛋白N-连接的寡糖上。在这里，我们发现两种形式的α 2，6-唾液酸转移酶由肝脏表达，并由两种不同的RNA编码，这两种RNA仅相差一个核苷酸。ST tyr在氨基酸123处具有Tyr，而ST cys在该位置处具有Cys。ST tyr比ST cys具有更高的催化活性;然而，当引入组织培养细胞时，两者都是功能性的。ST tyr和ST cys蛋白的蛋白水解加工和周转显著不同。ST cys在COS-1细胞中保持完整，而ST tyr被快速切割和分泌。对这些蛋白质的N-连接寡糖的分析表明，这两种蛋白质都进入晚期高尔基体。然而，ST tyr和ST cys蛋白水解加工的差异可能与其定位的差异有关，因为ST tyr而不是ST cys在细胞表面以低水平表达。ST tyr在后高尔基体隔室中被切割的可能性得到以下观察结果的支持：20 ° C温度阻断，其停止在反式高尔基体网络中的蛋白质转运，阻断ST tyr的切割和分泌。
The α2,6-sialyltransferase (ST) is a Golgi glycosyltransferase that adds sialic acid residues to glycoproteinN-linked oligosaccharides. Here we show that two forms of α2,6-sialyltransferase are expressed by the liver and are encoded by two different RNAs that differ by a single nucleotide. The ST tyr possesses a Tyr at amino acid 123, whereas the ST cys possesses a Cys at this position. The ST tyr is more catalytically active than the ST cys; however, both are functional when introduced into tissue culture cells. The proteolytic processing and turnover of the ST tyr and ST cys proteins differ dramatically. The ST cys is retained intact in COS-1 cells, whereas the ST tyr is rapidly cleaved and secreted. Analysis of theN-linked oligosaccharides of these proteins demonstrates that both proteins enter the late Golgi. However, differences in ST tyr and ST cys proteolytic processing may be related to differences in their localization, because ST tyr but not ST cys is expressed at low levels on the cell surface. The possibility that the ST tyr is cleaved in a post-Golgi compartment is supported by the observation that a 20°C temperature block, which stops protein transport in the trans Golgi network, blocks both cleavage and secretion of the ST tyr.