Division of Infectious Diseases, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
Departments of Cell and Molecular Biology and Biomedical and Pharmaceutical Sciences, University of Rhode Island, Kingston, Rhode Island, United States of America.
PLoS Pathog. 2020 Jun 3;16(6):e1008566. doi: 10.1371/journal.ppat.1008566. eCollection 2020 Jun.
Host-derived glutathione (GSH) is an essential source of cysteine for the intracellular pathogen Francisella tularensis. In a comprehensive transposon insertion sequencing screen, we identified several F. tularensis genes that play central and previously unappreciated roles in the utilization of GSH during the growth of the bacterium in macrophages. We show that one of these, a gene we named dptA, encodes a proton-dependent oligopeptide transporter that enables growth of the organism on the dipeptide Cys-Gly, a key breakdown product of GSH generated by the enzyme γ-glutamyltranspeptidase (GGT). Although GGT was thought to be the principal enzyme involved in GSH breakdown in F. tularensis, our screen identified a second enzyme, referred to as ChaC, that is also involved in the utilization of exogenous GSH. However, unlike GGT and DptA, we show that the importance of ChaC in supporting intramacrophage growth extends beyond cysteine acquisition. Taken together, our findings provide a compendium of F. tularensis genes required for intracellular growth and identify new players in the metabolism of GSH that could be attractive targets for therapeutic intervention.
宿主来源的谷胱甘肽（GSH）是细胞内病原体土拉弗朗西斯菌半胱氨酸的重要来源。在全面的转座子插入测序筛选中，我们鉴定了几种土拉弗朗西斯菌基因，这些基因在细菌在巨噬细胞中生长时利用 GSH 方面发挥着核心作用，以前未被认识到。我们表明，其中一个基因，我们称之为 dptA，编码一种质子依赖的寡肽转运蛋白，使生物体能够在二肽 Cys-Gly 上生长，这是由 γ-谷氨酰转肽酶（GGT）产生的 GSH 的关键分解产物。尽管 GGT 被认为是土拉弗朗西斯菌 GSH 分解的主要酶，但我们的筛选还鉴定了第二种酶，称为 ChaC，它也参与了外源性 GSH 的利用。然而，与 GGT 和 DptA 不同，我们表明 ChaC 在支持细胞内生长方面的重要性超出了半胱氨酸的获取。总之，我们的研究结果提供了土拉弗朗西斯菌基因的纲要，这些基因是细胞内生长所必需的，并确定了 GSH 代谢中的新参与者，这些参与者可能是治疗干预的有吸引力的靶点。
