Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, Mattenstrasse 26, Basel 4058, Switzerland.
Department of Biosystems Science and Engineering, Eidgenössische Technische Hochschule (ETH) Zürich, Mattenstrasse 26, Basel 4058, Switzerland; Collaborative Innovation Center of Advanced Microstructures, National Laboratory of Solid State Microstructure, Department of Physics, Nanjing University, 22 Hankou Road, Nanjing, Jiang Su 210093, China PR.
Structure. 2018 Jul 3;26(7):987-996.e3. doi: 10.1016/j.str.2018.04.017. Epub 2018 May 31.
The core component BamA of the β barrel assembly machinery (BAM) adopts several conformations, which are thought to facilitate the insertion and folding of β barrel proteins into the bacterial outer membrane. Which factors alter the stability of these conformations remains to be quantified. Here, we apply single-molecule force spectroscopy to characterize the mechanical properties of BamA from Escherichia coli. In contrast to the N-terminal periplasmic polypeptide-transport-associated (POTRA) domains, the C-terminal transmembrane β barrel domain of BamA is mechanically much more stable. Exposed to mechanical stress this β barrel stepwise unfolds β hairpins until unfolding has been completed. Thereby, the mechanical stabilities of β barrel and β hairpins are modulated by the POTRA domains, the membrane composition and the extracellular lid closing the β barrel. We anticipate that these differences in stability, which are caused by factors contributing to BAM function, promote conformations of the BamA β barrel required to insert and fold outer membrane proteins.
β 桶组装机制（BAM）的核心组件 BamA 采用了几种构象，这些构象被认为有助于将β桶蛋白插入到细菌外膜中并使其折叠。哪些因素会改变这些构象的稳定性还有待量化。在这里，我们应用单分子力谱技术来表征大肠杆菌 BamA 的力学特性。与 N 端周质多肽转运相关（POTRA）结构域不同，BamA 的 C 端跨膜β桶结构域在力学上要稳定得多。暴露于机械应力下，该β桶会逐步展开β发夹，直到展开完成。由此，β桶和β发夹的机械稳定性受到 POTRA 结构域、膜成分和关闭β桶的细胞外盖的调节。我们预计，这些由促进 BAM 功能的因素引起的稳定性差异会促进 BamAβ桶插入和折叠外膜蛋白所需的构象。
