Mycobacterium tuberculosis uses the ESAT-6 system-1/type VII (ESX-1) system for secretion of virulence proteins into the host cell, however the mechanism of virulence proteins secretion, molecular components and regulation of ESX-1 system are only partly understood. In the current study, we have analyzed the biological function and recognition mechanism between ESX-1 virulence EspC and EccA₁ ATPase proteins. The EspC enters into A549 human lung carcinoma cells and exhibited cytotoxicity, as observed in MTT Assay. To understand the recognition mechanism between EspC and EccA₁ ATPase, the EspC and EccA₁ mutants were generated based on EspC~EccA₁ interactions, as observed in molecular modeling. Binding analysis shows that EspC export arm interacts specifically to the β-hairpin insertion motif of the TPR domain of EccA₁ ATPase. Mutations in these epitopes lead to significant decrease/or abolish the binding between EspC and EccA₁ ATPase. Our study provides insight into biological function and recognition mechanism between EspC and EccA₁ ATPase, which can be used as target to prevent EspC secretion/ or in general virulence factor secretion by mycobacterial ESX-1 system.

中文翻译：

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结核分枝杆菌ESX-1分泌毒力因子EspC的功能及识别机制剖析

结核分枝杆菌使用 ESAT-6 system-1/type VII (ESX-1) 系统将毒力蛋白分泌到宿主细胞中，但对毒力蛋白分泌的机制、分子成分和 ESX-1 系统的调控仅部分了解. 在目前的研究中，我们分析了 ESX-1 毒力 EspC 和 EccA ₁ ATPase 蛋白之间的生物学功能和识别机制。EspC 进入 A549 人肺癌细胞并表现出细胞毒性，如在 MTT 分析中所观察到的。为了理解 EspC 和 EccA ₁ ATPase之间的识别机制，基于 EspC~EccA ₁生成了 EspC 和 EccA ₁突变体分子模型中观察到的相互作用。结合分析显示 EspC 输出臂与 EccA ₁ ATPase的 TPR 结构域的 β-发夹插入基序特异性相互作用。这些表位的突变导致 EspC 和 EccA ₁ ATPase之间的结合显着减少/或消除。我们的研究深入了解了 EspC 和 EccA ₁ ATPase之间的生物学功能和识别机制，可用作阻止 EspC 分泌 / 或分枝杆菌 ESX-1 系统一般毒力因子分泌的靶点。