Geller B L, Wickner W
J Biol Chem. 1985 Oct 25;260(24):13281-5.
Procoat, the precursor form of the major coat protein of coliphage M13, assembles into the Escherichia coli inner membrane and is cleaved to mature coat protein by leader peptidase. This assembly process has previously been reconstituted using lipids and purified leader peptidase in a cell-free protein synthesis reaction (Watts, C., Silver, P., and Wickner, W. (1981) Cell 25, 347-353; Ohno-Iwashita, Y., and Wickner, W. (1983) J. Biol. Chem. 258, 1895-1900). We now report that procoat can also cross a liposomal membrane composed of only purified phospholipids; leader peptidase is not needed to catalyze insertion. When procoat is synthesized in vitro in the presence of liposomes with encapsulated chymotrypsin, the procoat inserts spontaneously through the membrane and is degraded. The protease was shown by several criteria to be in the lumen of the liposomes. These results demonstrate that the precursor form of an E. coli integral membrane protein can cross a membrane without the aid of leader peptidase or any other membrane proteins.
原衣壳蛋白（Procoat）是大肠杆菌噬菌体M13主要衣壳蛋白的前体形式，它组装进入大肠杆菌内膜，并被前导肽酶切割成成熟的衣壳蛋白。此前，在无细胞蛋白质合成反应中，利用脂质和纯化的前导肽酶重建了这一组装过程（瓦茨，C.，西尔弗，P.，和维克纳，W.（1981年）《细胞》25卷，347 - 353页；大野岩下，Y.，和维克纳，W.（1983年）《生物化学杂志》258卷，1895 - 1900页）。我们现在报告，原衣壳蛋白也能穿过仅由纯化磷脂组成的脂质体膜；催化插入过程不需要前导肽酶。当在含有包封胰凝乳蛋白酶的脂质体存在的情况下体外合成原衣壳蛋白时，原衣壳蛋白会自发穿过膜并被降解。通过多种标准证明蛋白酶存在于脂质体腔内。这些结果表明，大肠杆菌整合膜蛋白的前体形式可以在没有前导肽酶或任何其他膜蛋白帮助的情况下穿过膜。
