英国利兹大学Radford, Sheena E.团队报道了蛋白质-脂质电荷相互作用控制外膜蛋白折叠成不对称膜。相关研究成果发表在2023年9月14日出版的《自然—化学》。

生物膜由形成双层的磷脂分子的两个小叶组成，每个小叶包含不同的脂质组成。这种不对称性是通过专门的生物化学途径在体内产生和维持的，但在体外创造稳定的不对称膜的困难限制了人们对双层不对称性如何调节膜蛋白的折叠、稳定性和功能的理解。

该文中，研究人员使用环糊精介导的脂质交换制备了具有不对称双层的脂质体，并表征了两种细菌外膜蛋白（OMPs）OmpA和BamA的稳定性和折叠动力学。研究发现，相对于具有相同膜组成的对称脂质体，脂质体外叶中的过量负电荷阻碍了它们的插入和折叠，而内叶中的过度负电荷加速了它们的折叠。利用分子动力学、突变分析和生物信息学，研究人员鉴定了一种对折叠和稳定性至关重要的带正电的贴片。

这些结果解释了了众所周知的OMP的“阳性外部”规则，并对体外和体内驱动OMP折叠和组装的机制提出了见解。生物膜是不对称的双层，但对这种不对称性如何调节膜蛋白折叠或稳定性知之甚少。现在，用细菌外膜蛋白进行的折叠和稳定性分析揭示了对不对称膜电荷分布的高度敏感性，以及有效折叠所需的蛋白质电荷匹配。

附：英文原文

Title: Protein–lipid charge interactions control the folding of outer membrane proteins into asymmetric membranes

Author: Machin, Jonathan M., Kalli, Antreas C., Ranson, Neil A., Radford, Sheena E.

Issue&Volume: 2023-09-14

Abstract: Biological membranes consist of two leaflets of phospholipid molecules that form a bilayer, each leaflet comprising a distinct lipid composition. This asymmetry is created and maintained in vivo by dedicated biochemical pathways, but difficulties in creating stable asymmetric membranes in vitro have restricted our understanding of how bilayer asymmetry modulates the folding, stability and function of membrane proteins. In this study, we used cyclodextrin-mediated lipid exchange to generate liposomes with asymmetric bilayers and characterize the stability and folding kinetics of two bacterial outer membrane proteins (OMPs), OmpA and BamA. We found that excess negative charge in the outer leaflet of a liposome impedes their insertion and folding, while excess negative charge in the inner leaflet accelerates their folding relative to symmetric liposomes with the same membrane composition. Using molecular dynamics, mutational analysis and bioinformatics, we identified a positively charged patch critical for folding and stability. These results rationalize the well-known ‘positive-outside’ rule of OMPs and suggest insights into the mechanisms that drive OMP folding and assembly in vitro and in vivo. Biological membranes are asymmetric bilayers, but little is known about how this asymmetry modulates membrane protein folding or stability. Now, folding and stability assays with bacterial outer membrane proteins reveal an exquisite sensitivity to asymmetric membrane charge distribution and a required matching of protein charge for efficient folding.

DOI: 10.1038/s41557-023-01319-6

Source: https://www.nature.com/articles/s41557-023-01319-6