Department of Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA.
Precision Medicine Center, Traditional Chinese Medicine Hospital affiliated with Southwest Medical University, Luzhou, China.
J Bacteriol. 2020 Jul 9;202(15). doi: 10.1128/JB.00132-20.
Scc4 (formerly CT663) engages the transcription machinery and the pathogenic type III secretion system (T3SS). Both machines are required for infection. These requirements and the limited ability for genetic manipulation in have hampered dissection of Scc4's contributions. Here, by developing bacterial systems that permit the controlled expression and stable maintenance of Scc4, we assess Scc4's effects on chlamydial growth phenotype, secretion, and the patterns of T3SS gene expression. Expressing Scc4 in lacking a T3SS injectisome causes a growth defect. This deficiency is rescued by overexpressing the β-subunit of RNA polymerase (RNAP) or by exploiting sigma 70 (σ) (homologous to chlamydial σ) mutants that strengthen the interaction between σ region 4 and the β-flap, confirming Scc4's distinction as a module of RNAP holoenzyme capable of modulating transcription. expressing Scc4 sustains a functional T3SS, through which CopN secretion is boosted by cooption of Scc4 and Scc1. Finally, conditional expression of Scc4 in results in fast expansion of the -containing vacuole and accelerated chlamydial development, coupled to selective up- or downregulation of gene expression from different T3SS genes. This work reveals, for the first time, the context-dependent action of Scc4 linking it to diverse protein networks in bacteria. It establishes that Scc4, when overexpressed, exerts incredible effects on chlamydial development by reinforcing control of the T3SS. The T3SS is a key virulence factor required for infection. The control of the T3SS has not been well studied in this obligate intracellular pathogen. Here, we show that Scc4 plays a major role for precise control of the pathogenic T3SS at the levels of gene expression and effector secretion through genetically separable protein networks, allowing a fast adaptive mode of development during infection in human epithelial cells.
Scc4（原 CT663）参与转录机制和致病的 III 型分泌系统（T3SS）。这两种机器都是感染所必需的。这些要求以及在 中进行遗传操作的有限能力阻碍了 Scc4 贡献的剖析。在这里，通过开发允许 Scc4 受控表达和稳定维持的细菌系统，我们评估了 Scc4 对衣原体生长表型、分泌和 T3SS 基因表达模式的影响。在缺乏 T3SS 注入体的 中表达 Scc4 会导致生长缺陷。通过过度表达 RNA 聚合酶（RNAP）的 β 亚基或利用增强 σ 区域 4 与 β 瓣之间相互作用的 σ70（σ）（类似于衣原体 σ）突变体来拯救这种缺陷，证实了 Scc4 作为 RNA 聚合酶全酶模块的独特性，能够调节转录。在 中表达 Scc4 维持了功能性的 T3SS，通过 Scc4 和 Scc1 的共转导，促进了 CopN 的分泌。最后，在 中条件性表达 Scc4 导致包含的空泡快速扩张，衣原体发育加速，同时不同 T3SS 基因的表达发生选择性上调或下调。这项工作首次揭示了 Scc4 的上下文相关作用，将其与细菌中的不同蛋白质网络联系起来。它表明，Scc4 在过度表达时，通过加强对 T3SS 的控制，对衣原体的发育产生了难以置信的影响。T3SS 是感染所必需的关键毒力因子。在这种专性细胞内病原体中，T3SS 的控制尚未得到很好的研究。在这里，我们表明 Scc4 通过在基因表达和效应子分泌水平上通过遗传上可分离的蛋白质网络发挥主要作用，对致病的 T3SS 进行精确控制，允许在感染人类上皮细胞期间以快速适应的模式进行 发展。
