In response to starvation, endospore-forming bacteria differentiate into stress-resistant spores that can remain dormant for years yet rapidly germinate and resume growth in response to nutrients. The small molecule dipicolinic acid (DPA) plays a central role in both the stress resistance of the dormant spore and its exit from dormancy during germination. The spoVA locus is required for DPA import during sporulation and has been implicated in its export during germination, but the molecular bases are unclear. Here, we define the minimal set of proteins encoded in the Bacillus subtilis spoVA operon required for DPA import and demonstrate that these proteins form a membrane complex. Structural modeling of these components combined with mutagenesis and in vivo analysis reveal that the C and Eb subunits form a membrane channel, while the D subunit functions as a cytoplasmic plug. We show that point mutations that impair the interactions between D and the C–Eb membrane complex reduce the efficiency of DPA import during sporulation and reciprocally accelerate DPA release during germination. Our data support a model in which DPA transport into spores involves cycles of unplugging and then replugging the C–Eb membrane channel, while nutrient detection during germination triggers DPA release by unplugging it.

中文翻译：

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SpoVA 膜复合物是孢子形成过程中二吡啶甲酸的输入和发芽过程中的输出所必需的

为了应对饥饿，形成内生孢子的细菌会分化成抗压孢子，这些孢子可以休眠多年，但会迅速发芽并恢复生长以响应营养。小分子吡啶二羧酸 (DPA) 在休眠孢子的抗逆性和萌发期间从休眠中退出都起着核心作用。spoVA基因座是孢子形成过程中 DPA 导入所必需的，并且与萌发过程中的 DPA 导出有关，但分子基础尚不清楚。在这里，我们定义了枯草芽孢杆菌 spoVA中编码的最小蛋白质集DPA 导入所需的操纵子，并证明这些蛋白质形成膜复合物。这些成分的结构建模结合诱变和体内分析表明，C 和 Eb 亚基形成膜通道，而 D 亚基起细胞质栓塞的作用。我们表明，损害 D 和 C-Eb 膜复合物之间相互作用的点突变会降低孢子形成过程中 DPA 导入的效率，并在发芽过程中相互加速 DPA 释放。我们的数据支持一个模型，在该模型中，DPA 转运到孢子中涉及拔掉然后重新插入 C-Eb 膜通道的循环，而发芽过程中的营养检测通过拔掉它来触发 DPA 释放。