Mycobacteria use type VII secretion systems (T7SSs) to translocate a wide range of proteins across their diderm cell envelope. These systems, also called ESX systems, are crucial for the viability and/or virulence of mycobacterial pathogens, including Mycobacterium tuberculosis and the fish pathogen Mycobacterium marinum . We have previously shown that the M. tuberculosis ESX‐5 system is unable to fully complement secretion in an M. marinum esx‐5 mutant, suggesting species specificity in secretion. In this study, we elaborated on this observation and established that the membrane ATPase EccC₅, possessing four (putative) nucleotide‐binding domains (NBDs), is responsible for this. By creating M. marinum‐M. tuberculosis EccC₅ chimeras, we observed both in M. marinum and in M. tuberculosis that secretion specificity of PE_PGRS proteins depends on the presence of the cognate linker 2 domain of EccC₅. This region connects NBD1 and NBD2 of EccC₅ and is responsible for keeping NBD1 in an inhibited state. Notably, the ESX‐5 substrate EsxN, predicted to bind to NBD3 on EccC₅, showed a distinct secretion profile. These results indicate that linker 2 is involved in species‐specific substrate recognition and might therefore be an additional substrate recognition site of EccC₅.

中文翻译：

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ESX-5 VII型底物的物种特异性分泌由EccC5的接头2确定。

分枝杆菌使用VII型分泌系统（T7SS）在其干细胞包膜中转移多种蛋白质。这些系统，也称为ESX系统，对于分枝杆菌病原体（包括结核分枝杆菌和鱼类病原体海洋分枝杆菌）的生存力和/或毒力至关重要。先前我们已经表明，结核分枝杆菌ESX-5系统无法完全补充海藻分枝杆菌esx-5突变体中的分泌，这暗示了分泌物中的物种特异性。在这项研究中，我们详细阐述了这一发现，并确定具有四个（假定的）核苷酸结合域（NBD）的膜ATPase EccC ₅对此负责。通过创建海藻分枝杆菌-结核分枝杆菌EccC ₅嵌合体，我们在海分枝杆菌和结核分枝杆菌中都观察到PE_PGRS蛋白的分泌特异性取决于EccC ₅同源连接子2结构域的存在。该区域连接EccC _5的NBD1和NBD2，负责将NBD1保持在禁止状态。值得注意的是，预计与EccC ₅上的NBD3结合的ESX-5底物EsxN显示出独特的分泌特征。这些结果表明，连接子2参与特定物种的底物识别，因此可能是EccC ₅的另一个底物识别位点。