Simonen M, Tarkka E, Puohiniemi R, Sarvas M
National Public Health Institute, Helsinki, Finland.
FEMS Microbiol Lett. 1992 Dec 15;100(1-3):233-41. doi: 10.1111/j.1574-6968.1992.tb14046.x.
The secretion of the outer membrane proteins OmpA and OmpF of Escherichia coli has previously been found to be blocked at an early intracellular step, when these proteins were fused to a bacillar signal sequence and expressed in Bacillus subtilis. We have now fused these proteins to long secretable polypeptides, the amino-terminal portions of alpha-amylase or beta-lactamase. In spite of this, no secretion of the fusion proteins was detected in B. subtilis. With the exception of a small fraction of the beta-lactamase fusion, the proteins were cell-bound with uncleaved signal sequences. Protease accessibility indicated that the fusion proteins were not even partially exposed on the outer surface of the cytoplasmic membrane. Thus there was no change of the location compared to the OmpA or OmpF fused to the signal sequence only. We conclude that, like OmpA and OmpF, the fusion proteins fold into an export-incompatible conformation in B. subtilis before the start of translocation, which we postulate to be a late post-translational event.
此前发现，当将大肠杆菌的外膜蛋白OmpA和OmpF与杆状信号序列融合并在枯草芽孢杆菌中表达时，其分泌在细胞内早期步骤就被阻断。我们现在已将这些蛋白与可分泌的长多肽（α-淀粉酶或β-内酰胺酶的氨基末端部分）融合。尽管如此，在枯草芽孢杆菌中未检测到融合蛋白的分泌。除了一小部分β-内酰胺酶融合蛋白外，这些蛋白与未切割信号序列结合在细胞上。蛋白酶可及性表明，融合蛋白甚至没有部分暴露在细胞质膜的外表面。因此，与仅与信号序列融合的OmpA或OmpF相比，其位置没有变化。我们得出结论，与OmpA和OmpF一样，融合蛋白在转运开始前在枯草芽孢杆菌中折叠成与输出不兼容的构象，我们推测这是一个翻译后晚期事件。
