Randall L L, Josefsson L G, Hardy S J
Biochem Soc Trans. 1980 Aug;8(4):413-5. doi: 10.1042/bst0080413a.
The mechanism of export of protein in E. coli can be summarized in terms of the 'signal hypothesis'. The proteins are synthesized on membrane-bound polyribosomes in the form of precursors, which carry N-terminal extensions of amino acids, the 'signal'. The proteins are vectorially transferred through the membrane during synthesis and the signal sequence is removed to generate the mature protein. The basic principle is established and it is now important to elucidate the molecular mechanism of export. We have attempted to detail the proteolytic removal of the signal. We have shown that the precursors are processed post-translationally, and we have data suggesting that two cleavages may be involved. It appears that processing is not necessary to activate the mature proteins. Why then is the signal removed? Perhaps the answer will shed light on the other yet unanswered questions: what is the energy source for the translocation? how does the cell differentiate between the two classes of exported proteins, those in the periplasm and those in the outer membrane? The next few years should see the resolution of these questions.
大肠杆菌中蛋白质的输出机制可以根据“信号假说”进行总结。蛋白质以前体的形式在膜结合多聚核糖体上合成，前体带有氨基酸的N端延伸部分，即“信号”。蛋白质在合成过程中通过膜进行定向转移，信号序列被去除以产生成熟蛋白质。基本原理已经确立，现在阐明输出的分子机制很重要。我们试图详细研究信号的蛋白水解去除过程。我们已经表明前体是在翻译后进行加工的，并且我们有数据表明可能涉及两次切割。似乎加工对于激活成熟蛋白质不是必需的。那么为什么信号会被去除呢？也许答案会为其他尚未解决的问题提供线索：转运的能量来源是什么？细胞如何区分两类输出蛋白，即周质中的蛋白和外膜中的蛋白？未来几年应该能够解决这些问题。
