Department of Microbiology, University of Washington, Seattle, Washington, USA.
Howard Hughes Medical Institute, Department of Pharmacology, University of Washington, Seattle, Washington, USA.
mBio. 2020 Feb 11;11(1):e03277-19. doi: 10.1128/mBio.03277-19.
The subsp. serovar Typhimurium PhoPQ two-component system is activated within the intracellular phagosome environment, where it promotes remodeling of the outer membrane and resistance to innate immune antimicrobial peptides. Maintenance of the PhoPQ-regulated outer membrane barrier requires PbgA, an inner membrane protein with a transmembrane domain essential for growth, and a periplasmic domain required for PhoPQ-activated increases in outer membrane cardiolipin. Here, we report the crystal structure of cardiolipin-bound PbgA, adopting a novel transmembrane fold that features a cardiolipin binding site in close proximity to a long and deep cleft spanning the lipid bilayer. The end of the cleft extends into the periplasmic domain of the protein, which is structurally coupled to the transmembrane domain via a functionally critical C-terminal helix. In conjunction with a conserved putative catalytic dyad situated at the middle of the cleft, our structural and mutational analyses suggest that PbgA is a multifunction membrane protein that mediates cardiolipin transport, a function essential for growth, and perhaps catalysis of an unknown enzymatic reaction. Gram-negative bacteria cause many types of infections and have become increasingly resistant to available antibiotic drugs. The outer membrane serves as an important barrier that protects bacteria against antibiotics and other toxic compounds. This outer membrane barrier function is regulated when bacteria are in host environments, and the protein PbgA contributes significantly to this increased barrier function by transporting cardiolipin to the outer membrane. We determined the crystal structure of PbgA in complex with cardiolipin and propose a model for its function. Knowledge of the mechanisms of outer membrane assembly and integrity can greatly contribute to the development of new and effective antibiotics, and this structural information may be useful in this regard.
鼠伤寒血清型 PhoPQ 亚亚种的双组分系统在细胞内吞噬体环境中被激活，在该环境中，它促进了外膜的重塑，并提高了对固有免疫抗菌肽的抗性。PhoPQ 调节的外膜屏障的维持需要 PbgA，PbgA 是一种具有跨膜结构域的内膜蛋白，该结构域对于生长是必需的，而周质域对于 PhoPQ 激活的外膜心磷脂的增加是必需的。在这里，我们报告了与心磷脂结合的 PbgA 的晶体结构，采用了一种新颖的跨膜折叠，其特征是在心磷脂结合位点附近有一个长而深的裂隙，跨越脂质双层。裂隙的末端延伸到蛋白质的周质域，该周质域通过功能关键的 C 端螺旋与跨膜域结构相连。结合位于裂隙中部的保守假定催化二联体，我们的结构和突变分析表明，PbgA 是一种多功能膜蛋白，可介导心磷脂转运，该功能对于生长至关重要，并且可能催化未知的酶反应。革兰氏阴性菌会引起多种类型的感染，并且对现有抗生素药物的耐药性越来越强。外膜作为一个重要的屏障，可保护细菌免受抗生素和其他有毒化合物的侵害。当细菌处于宿主环境中时，该外膜屏障功能会受到调节，而 PbgA 蛋白通过将心磷脂转运到外膜中，对这种增强的屏障功能做出了重要贡献。我们确定了 PbgA 与心磷脂复合物的晶体结构，并提出了其功能模型。了解外膜组装和完整性的机制可以极大地促进新型有效抗生素的开发，而这种结构信息可能对此有所帮助。
