大肠杆菌纯化的SecB蛋白在体外可延缓麦芽糖结合蛋白的折叠并促进其膜易位。
Purified secB protein of Escherichia coli retards folding and promotes membrane translocation of the maltose-binding protein in vitro.
作者信息
Weiss J B, Ray P H, Bassford P J
机构信息
Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill 27514.
出版信息
Proc Natl Acad Sci U S A. 1988 Dec;85(23):8978-82. doi: 10.1073/pnas.85.23.8978.
The efficient export of a subset of Escherichia coli envelope proteins is dependent upon the product of the secB gene. Previous studies indicated that SecB promotes the export of the periplasmic maltose-binding protein (MBP) by preventing premature folding of the precursor MBP in the cytoplasm into an export-incompetent form. In this study, SecB has been purified to homogeneity and shown to be a soluble, cytoplasmic, multimeric protein composed of identical 17-kDa subunits. SecB was required for efficient in vitro translocation of MBP into inverted membrane vesicles. The addition of purified SecB to an in vitro system prepared from SecB- cells significantly enhanced MBP translocation. The purified protein also quantitatively retarded folding of precursor MBP into a stable, protease-resistant conformation in the absence of membranes. Finally, the inclusion of excess purified SecB in a SecB+ in vitro system significantly prolonged the time in which precursor MBP remained competent for posttranslational import into membrane vesicles.
大肠杆菌包膜蛋白的一个子集的有效输出依赖于secB基因的产物。先前的研究表明，SecB通过防止前体麦芽糖结合蛋白（MBP）在细胞质中过早折叠成无输出能力的形式来促进周质麦芽糖结合蛋白（MBP）的输出。在本研究中，SecB已被纯化至同质，并显示为一种由相同的17 kDa亚基组成的可溶性、细胞质、多聚体蛋白。SecB是MBP在体外有效转运到倒膜囊泡所必需的。将纯化的SecB添加到由SecB缺陷细胞制备的体外系统中，可显著增强MBP的转运。在没有膜的情况下，纯化的蛋白还能定量地抑制前体MBP折叠成稳定的、抗蛋白酶的构象。最后，在SecB阳性体外系统中加入过量纯化的SecB，可显著延长前体MBP保持翻译后导入膜囊泡能力的时间。
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