Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore, Singapore.
Institut Pasteur, Unité de Microbiologie Structurale, Paris, France.
Microbiol Spectr. 2023 Aug 17;11(4):e0148123. doi: 10.1128/spectrum.01481-23. Epub 2023 Jul 11.
Streptococcus gallolyticus subsp. () is an opportunistic bacterial pathogen strongly associated with colorectal cancer. Here, through comparative genomics analysis, we demonstrated that the genetic locus encoding the type VIIb secretion system (T7SSb) machinery is uniquely present in in two different arrangements. UCN34 carrying the most prevalent T7SSb genetic arrangement was chosen as the reference strain. To identify the effectors secreted by this secretion system, we inactivated the gene encoding the motor of this machinery. A comparison of the proteins secreted by UCN34 wild type and its isogenic Δ mutant revealed six T7SSb effector proteins, including the expected WXG effector EsxA and three LXG-containing proteins. In this work, we characterized an LXG-family toxin named herein TelE promoting the loss of membrane integrity. Seven homologs of TelE harboring a conserved glycine zipper motif at the C terminus were identified in different isolates. Scanning mutagenesis of this motif showed that the glycine residue at position 470 was crucial for TelE membrane destabilization activity. TelE activity was antagonized by a small protein TipE belonging to the DUF5085 family. Overall, we report herein a unique T7SSb effector exhibiting a toxic activity against nonimmune bacteria. In this study, 38 clinical isolates of Streptococcus gallolyticus subsp. () were sequenced and a genetic locus encoding the type VIIb secretion system (T7SSb) was found conserved and absent from 16 genomes of the closely related S. gallolyticus subsp. (). The T7SSb is a bona fide pathogenicity island. Here, we report that the model organism strain UCN34 secretes six T7SSb effectors. One of the six effectors named TelE displayed a strong toxicity when overexpressed in Escherichia coli. Our results indicate that TelE is probably a pore-forming toxin whose activity can be antagonized by a specific immunity protein named TipE. Overall, we report a unique toxin-immunity protein pair and our data expand the range of effectors secreted through T7SSb.
无乳链球菌亚种（）是一种与结直肠癌密切相关的机会性细菌病原体。在这里，通过比较基因组学分析，我们证明了编码 VIIb 型分泌系统（T7SSb）机械的遗传基因座在两个不同的排列中独特存在于中。携带最常见 T7SSb 遗传排列的 UCN34 被选为参考菌株。为了确定该分泌系统分泌的效应物，我们使该机械的马达基因失活。UCN34 野生型和其同源缺失突变体分泌的蛋白质的比较揭示了六种 T7SSb 效应蛋白，包括预期的 WXG 效应物 EsxA 和三种含有 LXG 的蛋白。在这项工作中，我们表征了一种命名为 TelE 的 LXG 家族毒素，它促进膜完整性的丧失。在不同的中分离株中鉴定了七种含有保守甘氨酸拉链基序在 C 末端的 TelE 同源物。该基序的扫描诱变表明，位置 470 的甘氨酸残基对于 TelE 膜不稳定活性至关重要。TelE 活性被属于 DUF5085 家族的小蛋白 TipE 拮抗。总的来说，我们在此报告了一种独特的 T7SSb 效应物，它对非免疫细菌表现出毒性活性。 在这项研究中，对 38 株无乳链球菌亚种（）临床分离株进行了测序，并发现编码 VIIb 型分泌系统（T7SSb）的基因座在密切相关的无乳链球菌亚种（）的 16 个基因组中保守存在。T7SSb 是一个真正的致病性岛。在这里，我们报告模型生物 株 UCN34 分泌六种 T7SSb 效应物。在大肠杆菌中过表达的六种效应物之一 TelE 表现出很强的毒性。我们的结果表明，TelE 可能是一种形成孔的毒素，其活性可以被一种名为 TipE 的特定免疫蛋白拮抗。总的来说，我们报告了一个独特的毒素-免疫蛋白对，我们的数据扩展了通过 T7SSb 分泌的效应物范围。
