The Salmonella enterica subsp. enterica 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.IMPORTANCE 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.

中文翻译：

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PhoPQ 调节的外膜心磷脂增加所需的内膜蛋白的结构。


肠沙门氏菌亚种。鼠伤寒肠血清型 PhoPQ 双组分系统在细胞内吞噬体环境中被激活，促进外膜重塑和对先天免疫抗菌肽的抵抗。 PhoPQ 调节的外膜屏障的维持需要 PbgA，一种具有生长必需的跨膜结构域的内膜蛋白，以及 PhoPQ 激活的外膜心磷脂增加所需的周质结构域。在这里，我们报告了心磷脂结合的 PbgA 的晶体结构，采用一种新型跨膜折叠，其特点是心磷脂结合位点靠近跨越脂质双层的长而深的裂缝。裂口的末端延伸到蛋白质的周质结构域，该结构域通过功能关键的C端螺旋在结构上与跨膜结构域偶联。结合位于裂口中部的保守推定催化二元体，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，这是生长所必需的功能，并且可能催化未知的酶反应。 重要性革兰氏阴性细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。外膜是保护细菌免受抗生素和其他有毒化合物侵害的重要屏障。当细菌处于宿主环境中时，这种外膜屏障功能受到调节，并且蛋白质 PbgA 通过将心磷脂转运到外膜，对这种增强的屏障功能做出了显着贡献。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，并且这种结构信息在这方面可能很有用。