Etzkorn Manuel, Zoonens Manuela, Catoire Laurent J, Popot Jean-Luc, Hiller Sebastian
Institute of Physical Biology, Heinrich Heine University, Universitätsstr. 1, 40225, Düsseldorf, Germany.
J Membr Biol. 2014 Oct;247(9-10):965-70. doi: 10.1007/s00232-014-9657-9. Epub 2014 Mar 26.
Amphipathic polymers called amphipols provide a valuable alternative to detergents for keeping integral membrane proteins soluble in aqueous buffers. Here, we characterize spatial contacts of amphipol A8-35 with membrane proteins from two architectural classes: The 8-stranded β-barrel outer membrane protein OmpX and the α-helical protein bacteriorhodopsin. OmpX is well structured in A8-35, with its barrel adopting a fold closely similar to that in dihexanoylphosphocholine micelles. The accessibility of A8-35-trapped OmpX by a water-soluble paramagnetic molecule is highly similar to that in detergent micelles and resembles the accessibility in the natural membrane. For the α-helical protein bacteriorhodopsin, previously shown to keep its fold and function in amphipols, NMR data show that the imidazole protons of a polyhistidine tag at the N-terminus of the protein are exchange protected in the presence of detergent and lipid bilayer nanodiscs, but not in amphipols, indicating the absence of an interaction in the latter case. Overall, A8-35 exhibits protein interaction properties somewhat different from detergents and lipid bilayer nanodiscs, while maintaining the structure of solubilized integral membrane proteins.
被称为两性分子的两亲性聚合物为使整合膜蛋白在水性缓冲液中保持可溶提供了一种有价值的替代去污剂的方法。在这里，我们表征了两性分子A8-35与来自两种结构类型的膜蛋白的空间接触：8股β桶状外膜蛋白OmpX和α螺旋蛋白细菌视紫红质。OmpX在A8-35中结构良好，其桶状结构采用与二己酰磷脂酰胆碱胶束中非常相似的折叠方式。水溶性顺磁性分子对被A8-35捕获的OmpX的可及性与在去污剂胶束中的情况高度相似，并且类似于在天然膜中的可及性。对于α螺旋蛋白细菌视紫红质，先前已证明其在两性分子中能保持其折叠和功能，核磁共振数据表明，在蛋白质N端的多组氨酸标签的咪唑质子在去污剂和脂质双层纳米盘中存在时受到交换保护，但在两性分子中则不然，这表明在后一种情况下不存在相互作用。总体而言，A8-35表现出与去污剂和脂质双层纳米盘有些不同的蛋白质相互作用特性，同时保持了溶解的整合膜蛋白的结构。
