Wang Xiaoqiang, Huang Haihong, Sun Chenghao, Huang Fang
State Key Laboratory of Heavy Oil Processing and Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, China.
State Key Laboratory of Heavy Oil Processing and Center for Bioengineering and Biotechnology, China University of Petroleum (East China), Qingdao 266580, China.
J Colloid Interface Sci. 2015 Jan 1;437:170-180. doi: 10.1016/j.jcis.2014.09.007. Epub 2014 Sep 16.
Surfactants that can provide a more natural substitute for lipid bilayers are important in the purification and in vitro study of membrane proteins. Here we investigate the structural response of a model membrane protein, bacteriorhodopsin (BR), to phosphocholine biosurfactants. Phosphocholine biosurfactants are a type of biomimetic amphiphile that are similar to phospholipids, in which membrane proteins are commonly embedded. Multiple spectroscopic and zeta potential measurements are employed to characterize the conformational change, secondary and tertiary structure, oligomeric status, surface charge distribution and the structural stability of BR solubilized with phosphocholine biosurfactants of varying tail length. The process of phosphocholine micelle formation is found to facilitate the solubilization of BR, and for long-chain phosphocholines, concentrations much higher than their critical micelle concentrations achieve good solubilization. Phosphocholine biosurfactants are shown to be mild compared with the ionic surfactant SDS or CTAB, and tend to preserve membrane protein structure during solubilization, especially at low micelle concentrations, by virtue of their phospholipid-like zwitterionic head groups. The increase of alkyl chain length is shown to obviously enhance the capability of phosphocholine biosurfactants to stabilize BR. The underlying mechanism for the favorable actions of phosphocholine biosurfactant is also discussed.
能够为脂质双分子层提供更天然替代物的表面活性剂，在膜蛋白的纯化及体外研究中具有重要意义。在此，我们研究了一种模型膜蛋白——细菌视紫红质（BR）对磷酸胆碱生物表面活性剂的结构响应。磷酸胆碱生物表面活性剂是一类仿生两亲分子，与磷脂相似，而膜蛋白通常嵌入磷脂中。我们采用多种光谱和zeta电位测量方法，来表征用不同尾长的磷酸胆碱生物表面活性剂增溶的BR的构象变化、二级和三级结构、寡聚状态、表面电荷分布以及结构稳定性。研究发现，磷酸胆碱胶束的形成过程有助于BR的增溶，对于长链磷酸胆碱，浓度远高于其临界胶束浓度时就能实现良好的增溶效果。结果表明，与离子表面活性剂SDS或CTAB相比，磷酸胆碱生物表面活性剂较为温和，并且由于其类似磷脂的两性离子头部基团，在增溶过程中倾向于保持膜蛋白结构，尤其是在低胶束浓度下。研究表明，烷基链长度的增加明显增强了磷酸胆碱生物表面活性剂稳定BR的能力。我们还讨论了磷酸胆碱生物表面活性剂产生有利作用的潜在机制。
