Bielinska M, Grant G A, Boime I
J Biol Chem. 1978 Oct 25;253(20):7117-9.
To examine the relationship between pre-protein cleavage and nascent chain glycosylation placental mRNA was translated in a reconstituted ascites cell-free system containing microsomal membranes prepared from tunicamycin-treated or untreated ascites tumor cells. In the absence of membranes, first trimester RNA directed the synthesis of the pre-form of the alpha subunit of human chorionic gonadotropin, whereas, in the presence of normal membranes, first trimester RNA directed the synthesis of a glycosylated form of the alpha subunit. Cell-free lysates containing membranes derived from tunicamycin-treated cells synthesized an alpha subunit protein with little, if any, carbohydrate. This protein was apparently sequestered into membranes since it was resistant to the action of trypsin which was added after translation. The pre-peptide of the alpha subunit protein was removed by treated membranes as determined by amino acid sequence analyses. The non-glycosylated protein pre-placental lactogen was also cleaved to its mature form by tunicamycin membranes. These data strongly suggest that, in vitro, glycosylation is not obligatory for pre-protein cleavage and sequestration of these placental protein hormones.
为了研究前体蛋白切割与新生链糖基化之间的关系，胎盘mRNA在含有从衣霉素处理或未处理的腹水肿瘤细胞制备的微粒体膜的重组腹水无细胞系统中进行翻译。在没有膜的情况下，孕早期RNA指导人绒毛膜促性腺激素α亚基前体形式的合成，而在正常膜存在的情况下，孕早期RNA指导α亚基糖基化形式的合成。含有来自衣霉素处理细胞的膜的无细胞裂解物合成了几乎没有（如果有的话）碳水化合物的α亚基蛋白。这种蛋白显然被隔离在膜中，因为它对翻译后添加的胰蛋白酶的作用具有抗性。通过氨基酸序列分析确定，α亚基蛋白的前肽被处理过的膜去除。非糖基化的胎盘催乳素前体蛋白也被衣霉素处理的膜切割成其成熟形式。这些数据强烈表明，在体外，糖基化对于这些胎盘蛋白激素的前体蛋白切割和隔离不是必需的。
