School of Life Sciences, Arizona State University, Tempe, Arizona, USA.
Department of Chemistry, The Scripps Research Institute, Jupiter, Florida, USA.
J Bacteriol. 2020 Aug 25;202(18). doi: 10.1128/JB.00303-20.
LpxC is a deacetylase that catalyzes the first committed step of lipid A biosynthesis in LpxC competes for a common precursor, -3-hydroxymyristoyl-UDP-GlcNAc, with FabZ, whose dehydratase activity catalyzes the first committed step of phospholipid biosynthesis. To maintain the optimum flow of the common precursor to these two competing pathways, the LpxC level is controlled by FtsH/YciM-mediated proteolysis. It is not known whether this complex or another protein senses the status of lipid A synthesis to control LpxC proteolysis. The work carried out in this study began with a novel mutation, , which causes hypersensitivity to large antibiotics such as vancomycin and erythromycin. Isolates resistant to these antibiotics carried suppressor mutations in the and genes. Western blot analysis showed a dramatically reduced LpxC level in the background, while the presence of or suppressor mutations restored LpxC levels to different degrees. Based on these observations, it is proposed that YejM is a sensor of lipid A synthesis and controls LpxC levels by modulating the activity of the FtsH/YciM complex. The truncation of the periplasmic domain in the YejM1163 protein causes unregulated proteolysis of LpxC, thus diverting a greater pool of -3-hydroxymyristoyl-UDP-GlcNAc toward phospholipid synthesis. This imbalance in lipid synthesis perturbs the outer membrane permeability barrier, causing hypersensitivity toward vancomycin and erythromycin. suppressor mutations in and lower the proteolytic activity toward LpxC, thus restoring lipid homeostasis and the outer membrane permeability barrier. Lipid homeostasis is critical for proper envelope functions. The level of LpxC, which catalyzes the first committed step of lipopolysaccharide (LPS) synthesis, is controlled by an essential protease complex comprised of FtsH and YciM. Work carried out here suggests YejM, an essential envelope protein, plays a central role in sensing the state of LPS synthesis and controls LpxC levels by regulating the activity of FtsH/YciM. All four essential proteins are attractive targets of therapeutic development.
LpxC 是一种去乙酰化酶，催化脂多糖 (LPS) 生物合成的第一步。LpxC 与 FabZ 竞争共同的前体 -3-羟十七酰基-UDP-N-乙酰葡萄糖胺，FabZ 的脱水酶活性催化磷脂生物合成的第一步。为了使共同前体最优地流向这两条竞争途径，LpxC 水平受到 FtsH/YciM 介导的蛋白水解的控制。尚不清楚是该复合物还是另一种蛋白质感知脂多糖合成的状态来控制 LpxC 蛋白水解。本研究开展的工作始于一种新型突变体 ，该突变体导致对万古霉素和红霉素等大抗生素的超敏反应。对这些抗生素具有抗性的分离株在 和 基因中携带抑制突变。Western blot 分析显示，在 背景下 LpxC 水平显著降低，而 或 抑制突变的存在则以不同程度恢复 LpxC 水平。基于这些观察结果，提出 YejM 是脂多糖合成的传感器，通过调节 FtsH/YciM 复合物的活性来控制 LpxC 水平。YejM1163 蛋白的周质域截断导致 LpxC 的无调控蛋白水解，从而使更多的 -3-羟十七酰基-UDP-N-乙酰葡萄糖胺向磷脂合成转移。脂质合成的这种不平衡扰乱了外膜通透性屏障，导致对万古霉素和红霉素的超敏反应。 和 中的抑制突变降低了对 LpxC 的蛋白水解活性，从而恢复了脂质的动态平衡和外膜通透性屏障。脂质动态平衡对适当的包膜功能至关重要。催化脂多糖 (LPS) 合成第一步的 LpxC 的水平受到由 FtsH 和 YciM 组成的必需蛋白酶复合物的控制。这里开展的工作表明，必需膜蛋白 YejM 在感知 LPS 合成状态和通过调节 FtsH/YciM 活性控制 LpxC 水平方面发挥着核心作用。这四种必需蛋白都是治疗开发的有吸引力的靶点。
