Watkins Daniel W, Williams Sophie L, Collinson Ian
School of Biochemistry, University of Bristol, BS8 1TD, UK.
Present address: CytoSeek, Science Creates Old Market, Midland Road, Bristol, BS20JZ, UK.
Microbiology (Reading). 2022 Oct;168(10). doi: 10.1099/mic.0.001255.
The Gram-negative bacterial envelope is the first line of defence against environmental stress and antibiotics. Therefore, its biogenesis is of considerable fundamental interest, as well as a challenge to address the growing problem of antimicrobial resistance. All bacterial proteins are synthesised in the cytosol, so inner- and outer-membrane proteins, and periplasmic residents have to be transported to their final destinations via specialised protein machinery. The Sec translocon, a ubiquitous integral inner-membrane (IM) complex, is key to this process as the major gateway for protein transit from the cytosol to the cell envelope; this can be achieved during their translation, or afterwards. Proteins need to be directed into the inner-membrane (usually co-translational), otherwise SecA utilises ATP and the proton-motive-force (PMF) to drive proteins across the membrane post-translationally. These proteins are then picked up by chaperones for folding in the periplasm, or delivered to the β-barrel assembly machinery (BAM) for incorporation into the outer-membrane. The core hetero-trimeric SecYEG-complex forms the hub for an extensive network of interactions that regulate protein delivery and quality control. Here, we conduct a biochemical exploration of this 'secretosome' -a very large, versatile and inter-changeable assembly with the Sec-translocon at its core; featuring interactions that facilitate secretion (SecDF), inner- and outer-membrane protein insertion (respectively, YidC and BAM), protein folding and quality control (e.g. PpiD, YfgM and FtsH). We propose the dynamic interplay amongst these, and other factors, act to ensure efficient envelope biogenesis, regulated to accommodate the requirements of cell elongation and division. We believe this organisation is critical for cell wall biogenesis and remodelling and thus its perturbation could be a means for the development of anti-microbials.
革兰氏阴性菌的包膜是抵御环境压力和抗生素的第一道防线。因此，其生物发生不仅具有相当大的基础研究价值，对于应对日益严重的抗菌耐药性问题也是一项挑战。所有细菌蛋白都在细胞质中合成，因此内膜蛋白、外膜蛋白和周质蛋白必须通过专门的蛋白质转运机制运输到它们的最终目的地。Sec转位子是一种普遍存在的整合内膜（IM）复合物，是这一过程的关键，它是蛋白质从细胞质转运到细胞包膜的主要通道；这一过程可以在蛋白质翻译期间或之后完成。蛋白质需要被引导进入内膜（通常是共翻译过程），否则SecA会利用ATP和质子动力（PMF）在翻译后驱动蛋白质穿过膜。然后这些蛋白质被分子伴侣识别，以便在周质中折叠，或者被递送到β-桶组装机器（BAM）中，以便整合到外膜中。核心异源三聚体SecYEG复合物形成了一个广泛相互作用网络的中心，该网络调节蛋白质的输送和质量控制。在这里，我们对这个“分泌体”进行了生化探索——这是一个非常大的、多功能且可互换的组装体，其核心是Sec转位子；其特征在于促进分泌的相互作用（SecDF）、内膜和外膜蛋白插入（分别为YidC和BAM）、蛋白质折叠和质量控制（例如PpiD、YfgM和FtsH）。我们提出，这些因素与其他因素之间的动态相互作用，有助于确保高效的包膜生物发生，并进行调节以适应细胞伸长和分裂的需求。我们认为这种组织对于细胞壁的生物发生和重塑至关重要，因此对其进行干扰可能是开发抗菌药物的一种手段。
