脂多糖(LPS)是许多革兰氏阴性细菌的外膜(OM)的特殊成分,使这些细菌对许多有毒分子高度不可渗透。包括抗生素。LPS通过专用的膜间运输系统在OM处组装,LPT(LPS运输)机械,由位于内膜(IM)(LptB2CFG)中的七个必需蛋白组成,周质(LptA),和OM(LptDE)。LPS转运中的缺陷损害了LPS在OM处的插入和组装,并导致细胞包膜及其渗透屏障性质的整体改变。LptA是Lpt机器的关键组件。它通过与IM蛋白LptC和OM蛋白LptD相互作用连接IM和OM亚复合物,从而使LPS跨周质运输。Lpt系统装配中的缺陷导致LptA退化,其稳定性可以被认为是不正确装配的Lpt系统的标志。的确,其IM和OM对接点的LptA招募需要LptB2CFG和LptDE子复合体的正确成熟,分别。这些质量控制检查点对于避免LPS误定是至关重要的。为了进一步剖析整个Lpt跨包络桥组件的要求,我们通过使用抑制剂化合物阻断LPS的合成来探索LPS存在的重要性.这里,我们发现LPS合成的中断导致LptA和LptD的降解,这表明,在没有LPS底物的情况下,Lpt复合物的稳定性受到损害。在这些条件下,DegP,大肠杆菌中的一种主要伴侣蛋白酶,负责LptD而不是LptA退化。重要的是,LptD和LptA稳定性不受干扰LPS或肽聚糖层完整性的应激源影响,进一步支持以下观点:LPS底物对于保持Lpt跨包膜复合物的组装至关重要,并且LptA和LptD在Lpt系统的稳定性中起着重要作用。
Lipopolysaccharide (LPS) is a peculiar component of the outer membrane (OM) of many Gram-negative bacteria that renders these bacteria highly impermeable to many toxic molecules, including antibiotics. LPS is assembled at the OM by a dedicated intermembrane transport system, the Lpt (LPS transport) machinery, composed of seven essential proteins located in the inner membrane (IM) (LptB2CFG), periplasm (LptA), and OM (LptDE). Defects in LPS transport compromise LPS insertion and assembly at the OM and result in an overall modification of the cell envelope and its permeability barrier properties. LptA is a key component of the Lpt machine. It connects the IM and OM sub-complexes by interacting with the IM protein LptC and the OM protein LptD, thus enabling the LPS transport across the periplasm. Defects in Lpt system assembly result in LptA degradation whose stability can be considered a marker of an improperly assembled Lpt system. Indeed, LptA recruitment by its IM and OM docking sites requires correct maturation of the LptB2CFG and LptDE sub-complexes, respectively. These quality control checkpoints are crucial to avoid LPS mistargeting. To further dissect the requirements for the complete Lpt transenvelope bridge assembly, we explored the importance of LPS presence by blocking its synthesis using an inhibitor compound. Here, we found that the interruption of LPS synthesis results in the degradation of both LptA and LptD, suggesting that, in the absence of the LPS substrate, the stability of the Lpt complex is compromised. Under these conditions, DegP, a major chaperone-protease in Escherichia coli, is responsible for LptD but not LptA degradation. Importantly, LptD and LptA stability is not affected by stressors disturbing the integrity of LPS or peptidoglycan layers, further supporting the notion that the LPS substrate is fundamental to keeping the Lpt transenvelope complex assembled and that LptA and LptD play a major role in the stability of the Lpt system.