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Abstract：
Salmonella enterica serovar Typhimurium (S. Typhimurium) controls lipopolysaccharide (LPS) biosynthesis by regulating proteolysis of LpxC, the rate-limiting enzyme and target of preclinical antibiotics. PbgA/YejM/LapC regulates LpxC levels and controls outer membrane (OM) LPS composition at the log-to-stationary phase transition. Suppressor substitutions in LPS assembly protein B (LapB/YciM) rescue the LPS and OM integrity defects of pbgA-mutant S. Typhimurium. We hypothesized that PbgA regulates LpxC proteolysis by controlling LapB\'s ability to bind LpxC as a function of the growth phase. According to existing models, when nutrients are abundant, PbgA binds and restricts LapB from interacting with LpxC and FtsH, which limits LpxC proteolysis. However, when nutrients are limited, there is debate whether LapB dissociates from PbgA to bind LpxC and FtsH to enhance degradation. We sought to examine these models and investigate how the structure of LapB enables salmonellae to control LpxC proteolysis and LPS biosynthesis. Salmonellae increase LapB levels during the stationary phase to promote LpxC degradation, which limits lipid A-core production and increases their survival. The deletion of lapB, resulting in unregulated lipid A-core production and LpxC overabundance, leads to bacterial growth retardation. Tetratricopeptide repeats near the cytosol-inner membrane interface are sufficient for LapB to bind LpxC, and remarkably, LapB and PbgA interact in both growth phases, yet LpxC only associates with LapB in the stationary phase. Our findings support that PbgA-LapB exists as a constitutive complex in S. Typhimurium, which differentially binds LpxC to control LpxC proteolysis and limit lipid A-core biosynthesis in response to changes in the environment.IMPORTANCEAntimicrobial resistance has been a costly setback for human health and agriculture. Continued pursuit of new antibiotics and targets is imperative, and an improved understanding of existing ones is necessary. LpxC is an essential target of preclinical trial antibiotics that can eliminate multidrug-resistant Gram-negative bacterial infections. LapB is a natural LpxC inhibitor that targets LpxC for degradation and limits lipopolysaccharide production in Enterobacteriaceae. Contrary to some studies, findings herein support that LapB remains in complex instead of dissociating from its presumed negative regulator, PbgA/YejM/LapC, under conditions where LpxC proteolysis is enhanced. Advanced comprehension of this critical protein-lipid signaling network will lead to future development and refinement of small molecules that can specifically interfere.
摘要：
肠病沙门氏菌（S.鼠伤寒）通过调节LpxC的蛋白水解来控制脂多糖（LPS）的生物合成，限速酶和临床前抗生素的目标。PbgA/YejM/LapC调节LpxC水平，并在对数到固定相转变时控制外膜（OM）LPS组成。LPS组装蛋白B(LapB/YciM)中的抑制物取代拯救pbgA-突变体鼠伤寒沙门氏菌的LPS和OM完整性缺陷。我们假设PbgA通过控制LapB结合LpxC的能力作为生长期的函数来调节LpxC蛋白水解。根据现有模型，当营养丰富时，PbgA结合并限制LapB与LpxC和FtsH相互作用，这限制了LpxC蛋白水解。然而,当营养有限时，LapB是否与PbgA解离以结合LpxC和FtsH以增强降解存在争议。我们试图检查这些模型并研究LapB的结构如何使沙门氏菌控制LpxC蛋白水解和LPS生物合成。沙门氏菌在固定阶段增加LapB水平以促进LpxC降解，这限制了脂质A核心的产生并增加了它们的存活率。lapB的删除,导致脂质A核心产生不受调节和LpxC过量，导致细菌生长迟缓。胞质溶胶-内膜界面附近的四肽重复序列足以使LapB结合LpxC，值得注意的是，LapB和PbgA在两个生长阶段都相互作用，然而，LpxC仅在固定阶段与LapB相关。我们的发现支持PbgA-LapB在鼠伤寒沙门氏菌中作为组成复合物存在，差异结合LpxC以控制LpxC蛋白水解并限制脂质A核心生物合成以响应环境的变化。抗生素耐药性一直是人类健康和农业的代价高昂的挫折。继续追求新的抗生素和目标势在必行，并且有必要对现有的更好的理解。LpxC是临床试验前抗生素的重要目标，可以消除多药耐药的革兰氏阴性菌感染。LapB是一种天然的LpxC抑制剂,其靶向LpxC降解并限制肠杆菌科中脂多糖的产生。与一些研究相反，本文的研究结果支持LapB保持复杂状态，而不是与其假定的负调节剂分离，PbgA/YejM/LapC,在LpxC蛋白水解增强的条件下。对这种关键的蛋白质-脂质信号网络的深入理解将导致未来的开发和完善可以特异性干扰的小分子。
