Mechanobiology Institute, T-Lab, National University of Singapore, Singapore, Singapore.
Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, United States.
Elife. 2019 Apr 29;8:e45311. doi: 10.7554/eLife.45311.
After is phagocytosed, it resides in an acidic vacuole. Its cytoplasm acidifies to pH 5.6; acidification activates pathogenicity island 2 (SPI-2). SPI-2 encodes a type three secretion system whose effectors modify the vacuole, driving endosomal tubulation. Using super-resolution imaging in single bacterial cells, we show that low pH induces expression of the SPI-2 SsrA/B signaling system. Single particle tracking, atomic force microscopy, and single molecule unzipping assays identified pH-dependent stimulation of DNA binding by SsrB. A so-called phosphomimetic form (D56E) was unable to bind to DNA in live cells. Acid-dependent DNA binding was not intrinsic to regulators, as PhoP and OmpR binding was not pH-sensitive. The low level of SPI-2 injectisomes observed in single cells is not due to fluctuating SsrB levels. This work highlights the surprising role that acid pH plays in virulence and intracellular lifestyles of ; modifying acid survival pathways represents a target for inhibiting .
被吞噬后，它存在于一个酸性液泡中。其细胞质酸化至 pH5.6；酸化激活致病岛 2（SPI-2）。SPI-2 编码一种三型分泌系统，其效应物修饰液泡，驱动内体小管化。通过在单个细菌细胞中的超分辨率成像，我们表明低 pH 诱导 SPI-2 SsrA/B 信号系统的表达。单颗粒跟踪、原子力显微镜和单分子解拉链试验确定了 SsrB 的 pH 依赖性 DNA 结合刺激。一种所谓的磷酸模拟形式（D56E）不能在活细胞中与 DNA 结合。依赖于 pH 的 DNA 结合不是调节剂所固有的，因为 PhoP 和 OmpR 结合对 pH 不敏感。在单细胞中观察到的低水平 SPI-2 注入器不是由于 SsrB 水平波动所致。这项工作强调了酸 pH 在毒力和细菌体内生活方式中的惊人作用；修饰酸存活途径是抑制的目标。
