Biotechnology Center, University of Technology, Tatzberg 47, 01307 Dresden, Germany.
J Mol Biol. 2010 Feb 26;396(3):610-6. doi: 10.1016/j.jmb.2009.12.034. Epub 2009 Dec 28.
A gating mechanism of the beta-barrel-forming outer membrane protein G (OmpG) from Escherichia coli was recently presented. The mechanism was based on X-ray structures revealed from crystals grown from solubilized OmpG at both neutral pH and acidic pH. To investigate whether these conformations represent the naturally occurring gating mechanism, we reconstituted OmpG in native E. coli lipids and applied high-resolution atomic force microscopy. The reconstituted OmpG molecules assembled into both monomers and dimers. Single monomeric and dimeric OmpG molecules showed open channel entrances at pH 7.5 and at room temperature. The extracellular loops connecting the beta-strands that form the transmembrane beta-barrel pore exhibited elevated structural flexibility. Upon lowering the pH to 5.0, the conformation of OmpG molecules changed to close the extracellular entrance of their channel. It appears that one or more of the extracellular loops collapsed onto the channel entrance. This conformational change was fully reversible. Our data confirm that the previously reported gating mechanism of OmpG occurs at physiological conditions in E. coli lipid membranes.
最近提出了一种大肠杆菌β-桶状膜蛋白 G（OmpG）的门控机制。该机制基于从中性 pH 和酸性 pH 下溶解的 OmpG 晶体生长揭示的 X 射线结构。为了研究这些构象是否代表自然发生的门控机制，我们在天然大肠杆菌脂质中重新构建了 OmpG，并应用了高分辨率原子力显微镜。重新构建的 OmpG 分子组装成单体和二聚体。在 pH 7.5 和室温下，单体和二聚体的单分子 OmpG 显示出开放的通道入口。连接形成跨膜β-桶孔的β-链的细胞外环表现出较高的结构灵活性。当 pH 降低至 5.0 时，OmpG 分子的构象发生变化，关闭通道的细胞外入口。似乎一个或多个细胞外环坍塌在通道入口上。这种构象变化是完全可逆的。我们的数据证实，先前报道的 OmpG 门控机制在大肠杆菌脂质膜的生理条件下发生。
