Lipopolysaccharide (LPS) resides in the outer membrane of Gram-negative bacteria where it is responsible for barrier function 1 , 2 . LPS can cause death as a result of septic shock, and its lipid A core is the target of polymyxin antibiotics 3 , 4 . Despite the clinical importance of polymyxins and the emergence of multidrug resistant strains 5 , our understanding of the bacterial factors that regulate LPS biogenesis is incomplete. Here we characterize the inner membrane protein PbgA and report that its depletion attenuates the virulence of Escherichia coli by reducing levels of LPS and outer membrane integrity. In contrast to previous claims that PbgA functions as a cardiolipin transporter 6 – 9 , our structural analyses and physiological studies identify a lipid A-binding motif along the periplasmic leaflet of the inner membrane. Synthetic PbgA-derived peptides selectively bind to LPS in vitro and inhibit the growth of diverse Gram-negative bacteria, including polymyxin-resistant strains. Proteomic, genetic and pharmacological experiments uncover a model in which direct periplasmic sensing of LPS by PbgA coordinates the biosynthesis of lipid A by regulating the stability of LpxC, a key cytoplasmic biosynthetic enzyme 10 – 12 . In summary, we find that PbgA has an unexpected but essential role in the regulation of LPS biogenesis, presents a new structural basis for the selective recognition of lipids, and provides opportunities for future antibiotic discovery. Structural and physiological studies show that the inner membrane protein PbgA is a crucial sensor of lipopolysaccharide (LPS) and regulates the activity of the LPS biosynthesis enzyme LpxC.

中文翻译：

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必需内膜脂多糖-PbgA 复合物的结构

脂多糖 (LPS) 位于革兰氏阴性菌的外膜中，负责屏障功能 1, 2。LPS 可因感染性休克而导致死亡，其脂质 A 核心是多粘菌素抗生素的靶点 3 、 4 。尽管多粘菌素的临床重要性和多重耐药菌株的出现 5 ，我们对调节 LPS 生物发生的细菌因素的理解是不完整的。在这里，我们表征了内膜蛋白 PbgA，并报告说它的消耗通过降低 LPS 和外膜完整性的水平来减弱大肠杆菌的毒力。与先前声称 PbgA 作为心磷脂转运蛋白 6-9 的说法相反，我们的结构分析和生理学研究确定了沿着内膜周质小叶的脂质 A 结合基序。合成的 PbgA 衍生肽在体外选择性地与 LPS 结合并抑制多种革兰氏阴性菌的生长，包括多粘菌素抗性菌株。蛋白质组学、遗传学和药理学实验揭示了一个模型，其中 PbgA 对 LPS 的直接周质传感通过调节 LpxC（一种关键的细胞质生物合成酶 10-12）的稳定性来协调脂质 A 的生物合成。总之，我们发现 PbgA 在 LPS 生物发生的调节中具有意想不到但必不可少的作用，为脂质的选择性识别提供了新的结构基础，并为未来的抗生素发现提供了机会。结构和生理研究表明，内膜蛋白 PbgA 是脂多糖 (LPS) 的关键传感器，可调节 LPS 生物合成酶 LpxC 的活性。