Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit Amsterdam, Amsterdam, The Netherlands.
Department of Medical Microbiology and Infection Control, Amsterdam UMC, Location VU Medical Center, Amsterdam, The Netherlands.
mBio. 2021 Mar 2;12(2):e02983-20. doi: 10.1128/mBio.02983-20.
CpnT, a NAD glycohydrolase, is the only known toxin that is secreted by CpnT is composed of two domains; the C-terminal domain is the toxin, whereas the N-terminal domain is required for secretion. CpnT shows characteristics of type VII secretion (T7S) substrates, including a predicted helix-turn-helix domain followed by a secretion motif (YxxxE). Disruption of this motif indeed abolished CpnT secretion. By analyzing different mutants, we established that CpnT is specifically secreted by the ESX-5 system in under axenic conditions and during macrophage infection. Surprisingly, intracellular secretion of CpnT was also dependent on both ESX-1 and ESX-4. These secretion defects could be partially rescued by coinfection with wild-type bacteria, indicating that secreted effectors are involved in this process. In summary, our data reveal that three different type VII secretion systems have to be functional in order to observe intracellular secretion of the toxin CpnT. For decades, it was believed that the intracellular pathogen does not possess toxins. Only fairly recently it was discovered that CpnT is a potent secreted toxin of , causing necrotic cell death in host cells. However, until now the secretion pathway remained unknown. In our study, we were able to identify CpnT as a substrate of the mycobacterial type VII secretion system. Pathogenic mycobacteria have up to five different type VII secretion systems, called ESX-1 to ESX-5, which play distinct roles for the pathogen during growth or infection. We were able to elucidate that CpnT is exclusively secreted by the ESX-5 system in bacterial culture. However, to our surprise we discovered that, during infection studies, CpnT secretion relies on intact ESX-1, ESX-4, and ESX-5 systems. We elucidate for the first time the intertwined interplay of three different and independent secretion systems to secrete one substrate during infection.
Cpnt,一种 NAD 糖基水解酶,是唯一已知的由 Cpnt 分泌的毒素。Cpnt 由两个结构域组成;C 端结构域是毒素,而 N 端结构域是分泌所必需的。Cpnt 表现出 VII 型分泌(T7S)底物的特征,包括一个预测的螺旋-转角-螺旋结构域,后面跟着一个分泌基序(YxxxE)。确实,破坏这个基序会使 Cpnt 无法分泌。通过分析不同的突变体,我们确定 Cpnt 是在 菌在缺氧条件下和巨噬细胞感染过程中由 ESX-5 系统特异性分泌的。令人惊讶的是,Cpnt 的细胞内分泌也依赖于 ESX-1 和 ESX-4。通过与野生型细菌共感染,可以部分挽救这些分泌缺陷,表明分泌效应物参与了这一过程。总之,我们的数据揭示了三个不同的 VII 型分泌系统必须发挥功能,才能观察到毒素 Cpnt 的细胞内分泌。几十年来,人们一直认为细胞内病原体 不具有毒素。直到最近才发现 Cpnt 是一种强效的分泌毒素,能导致宿主细胞坏死。然而,到目前为止,其分泌途径仍不清楚。在我们的研究中,我们能够鉴定出 Cpnt 是一种分枝杆菌 VII 型分泌系统的底物。致病性分枝杆菌有多达五个不同的 VII 型分泌系统,称为 ESX-1 到 ESX-5,它们在生长或感染过程中对病原体起着不同的作用。我们能够阐明 Cpnt 在细菌培养物中是由 ESX-5 系统专门分泌的。然而,令我们惊讶的是,我们发现,在感染研究中,Cpnt 的分泌依赖于完整的 ESX-1、ESX-4 和 ESX-5 系统。我们首次阐明了三个不同的和独立的分泌系统在感染过程中相互交织,以分泌一种底物。
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