The cell envelope of gram-negative bacteria, a structure comprising an outer (OM) and an inner (IM) membrane, is essential for life. The OM and the IM are separated by the periplasm, a compartment that contains the peptidoglycan. The OM is tethered to the peptidoglycan via the lipoprotein, Lpp. However, the importance of the envelope’s multilayered architecture remains unknown. Here, when we removed physical coupling between the OM and the peptidoglycan, cells lost the ability to sense defects in envelope integrity. Further experiments revealed that the critical parameter for the transmission of stress signals from the envelope to the cytoplasm, where cellular behaviour is controlled, is the IM-to-OM distance. Augmenting this distance by increasing the length of the lipoprotein Lpp destroyed signalling, whereas simultaneously increasing the length of the stress-sensing lipoprotein RcsF restored signalling. Our results demonstrate the physiological importance of the size of the periplasm. They also reveal that strict control over the IM-to-OM distance is required for effective envelope surveillance and protection, suggesting that cellular architecture and the structure of transenvelope protein complexes have been evolutionarily co-optimised for correct function. Similar strategies are likely at play in cellular compartments surrounded by 2 concentric membranes, such as chloroplasts and mitochondria.

革兰氏阴性细菌的细胞膜是生命必不可少的结构，革兰氏阴性细菌的细胞膜包括外膜（OM）和内膜（IM）。OM和IM被周质分隔开，周质是包含肽聚糖的区域。OM通过脂蛋白Lpp拴在肽聚糖上。但是，信封的多层体系结构的重要性仍然未知。在这里，当我们去除OM和肽聚糖之间的物理偶联时，细胞失去了感知包膜完整性缺陷的能力。进一步的实验表明，压力信号从包膜到细胞质的传递的关键参数是IM到OM的距离，其中细胞的行为受到控制。通过增加脂蛋白Lpp破坏信号的长度来增加该距离，而同时增加压力感应脂蛋白RcsF的长度可恢复信号传导。我们的结果证明了周质大小的生理重要性。他们还揭示了对IM-OM距离的严格控制对于有效的包膜监视和保护是必需的，这表明细胞结构和跨包膜蛋白复合物的结构已在进化上共同优化以实现正确的功能。类似的策略可能在由2个同心膜包围的细胞隔室中起作用，例如叶绿体和线粒体。他们还揭示了对IM-OM距离的严格控制对于有效的包膜监视和保护是必需的，这表明细胞结构和跨包膜蛋白复合物的结构已在进化上共同优化以实现正确的功能。类似的策略可能在由2个同心膜包围的细胞隔室中起作用，例如叶绿体和线粒体。他们还揭示了对IM-OM距离的严格控制对于有效的包膜监视和保护是必需的，这表明细胞结构和跨包膜蛋白复合物的结构已在进化上共同优化以实现正确的功能。类似的策略可能在由2个同心膜包围的细胞隔室中起作用，例如叶绿体和线粒体。