The molecular chaperone SecB is released from the carboxy-terminus of SecA during initiation of precursor protein translocation
The molecular chaperone SecB is released from the carboxy-terminus of SecA during initiation of precursor protein translocation
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DOI：
10.1093/emboj/16.20.6105
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发表时间：
1997-10-15
期刊：
影响因子：
11.4
通讯作者：
Driessen, AJM
中科院分区：
文献类型：
--
作者：
Fekkes, P;vanderDoes, C;Driessen, AJM
分子伴侣SecB使前体蛋白处于易位能力状态，并将它们靶向于大肠杆菌细胞膜上易位部位的SecA。SecA被认为是通过其羧基末端识别SecB的。为了确定SecB结合位点的最低要求，在谷胱甘肽-S-转移酶与SecA羧基末端不同部分之间构建了融合蛋白，并对其SecB结合进行了分析。一个惊人的短氨基酸序列对应于SecA最远端的22个氨基酰基残基，就足以与SecB或SecB-前体蛋白复合体真正结合。缺失这个高度保守结构域的缺失突变体SecAN880仍然支持前体蛋白易位，但不能结合SecB。野生型SecA和SecAN880的杂二聚体在与SecB结合时存在缺陷，表明SecA二聚体的两个羧基末端都需要形成真正的SecB结合位点。在蛋白质转位的非常早期阶段，SecB从转位酶中释放出来。当膜结合的SecA与ATP结合启动转位时，我们得出结论：SecA上的SecB结合部位局限于SecA二聚体的极端羧基末端，而SecB在转位开始时就从这个位置释放。
The chaperone SecB keeps precursor proteins in a translocation-competent state and targets them to SecA at the translocation sites in the cytoplasmic membrane of Escherichia coli. SecA is thought to recognize SecB via its carboxy-terminus. To determine the minimal requirement for a SecB-binding site, fusion proteins were created between glutathione-S-transferase and different parts of the carboxy-terminus of SecA and analysed for SecB binding. A strikingly short amino acid sequence corresponding to only the most distal 22 aminoacyl residues of SecA suffices for the authentic binding of SecB or the SecB-precursor protein complex. SecAN880, a deletion mutant that lacks this highly conserved domain, still supports precursor protein translocation but is unable to bind SecB. Heterodimers of wild-type SecA and SecAN880 are defective in SecB binding, demonstrating that both carboxy-termini of the SecA dimer are needed to form a genuine SecB-binding site. SecB is released from the translocase at a very early stage in protein translocation when the membrane-bound SecA binds ATP to initiate translocation, It is concluded that the SecB-binding site on SecA is confined to the extreme carboxy-terminus of the SecA dimer, and that SecB is released from this site at the onset of translocation.