General secretion signal for the mycobacterial type VII secretion pathway
General secretion signal for the mycobacterial type VII secretion pathway
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DOI：
10.1073/pnas.1119453109
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发表时间：
2012-07-10
影响因子：
11.1
通讯作者：
Bitter, Wilbert
中科院分区：
文献类型：
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作者：
Daleke, Maria H.;Ummels, Roy;Bitter, Wilbert
分枝杆菌病原体使用专门的VII型分泌（T7 S）系统将关键的毒力因子穿过其不寻常的细胞包膜转运到受感染的宿主细胞中。这些毒力因子缺乏经典的分泌信号，底物识别的机制还不清楚。在这里，我们证明了模型T7 S底物PE 25/PPE 41，形成异二聚体，通过位于PE 25的C末端的信号靶向T7 S途径ESX-5。该C末端内残基的定点诱变导致鉴定出高度保守的基序，即，YxxxD/E，这是分泌所必需的。该基序也是另一种ESX-5底物LipY分泌所必需的。致病性分枝杆菌有几种不同的T7 S系统，我们鉴定了ESX-1系统分泌的PE蛋白，这使我们能够比较这两种T7 S系统的底物识别。令人惊讶的是，该ESX-1底物含有功能上等同于PE 25的C-末端信号。PE蛋白之间的这些C-末端分泌信号的交换恢复了分泌，但每种PE蛋白通过其自身的ESX分泌系统保持分泌，表明额外的信号提供了系统特异性。值得注意的是，YxxxD/E基序也存在于ESX-1底物CFP-10和EspB中，并且是ESX-1底物CFP-10和EspB有效分泌所需的。因此，我们的数据表明，YxxxD/E基序是一种普遍的分泌信号，存在于所有已知的分枝杆菌T7 S底物或底物复合物。
Mycobacterial pathogens use specialized type VII secretion (T7S) systems to transport crucial virulence factors across their unusual cell envelope into infected host cells. These virulence factors lack classical secretion signals and the mechanism of substrate recognition is not well understood. Here we demonstrate that the model T7S substrates PE25/PPE41, which form a heterodimer, are targeted to the T7S pathway ESX-5 by a signal located in the C terminus of PE25. Site-directed mutagenesis of residues within this C terminus resulted in the identification of a highly conserved motif, i.e., YxxxD/E, which is required for secretion. This motif was also essential for the secretion of LipY, another ESX-5 substrate. Pathogenic mycobacteria have several different T7S systems and we identified a PE protein that is secreted by the ESX-1 system, which allowed us to compare substrate recognition of these two T7S systems. Surprisingly, this ESX-1 substrate contained a C-terminal signal functionally equivalent to that of PE25. Exchange of these C-terminal secretion signals between the PE proteins restored secretion, but each PE protein remained secreted via its own ESX secretion system, indicating that an additional signal(s) provides system specificity. Remarkably, the YxxxD/E motif was also present in and required for efficient secretion of the ESX-1 substrates CFP-10 and EspB. Therefore, our data show that the YxxxD/E motif is a general secretion signal that is present in all known mycobacterial T7S substrates or substrate complexes.