Influence of Gb3 glycosphingolipids differing in their fatty acid chain on the phase behaviour of solid supported membranes: chemical syntheses and impact of Shiga toxin binding
作者:Ole M. Schütte、Annika Ries、Alexander Orth、Lukas J. Patalag、Winfried Römer、Claudia Steinem、Daniel B. Werz
DOI:10.1039/c4sc01290a
日期:——
The Shiga toxin B subunit (STxB), which is involved in cell membrane attachment and trafficking of Shiga holotoxin, binds specifically to the glycosphingolipid Gb3. In biological membranes, Gb3 glycosphingolipids differ in their fatty acid composition and there is strong evidence that the fatty acid alters the binding behaviour of STxB as well as the intracellular routing of the Shiga toxin/Gb3 complex. To analyse the binding of STxB to different Gb3s, we chemically synthesized saturated, unsaturated, α-hydroxylated Gb3s and a combination thereof, all based on a C24-fatty acid chain starting from monosaccharide building blocks, sphingosine and the respective fatty acids. These chemically well-defined Gb3s were inserted into solid supported phase-separated lipid bilayers composed of DOPC/sphingomyelin/cholesterol as a simple mimetic of the outer leaflet of animal cell membranes. By fluorescence- and atomic force microscopy the phase behaviour of the bilayer as well as the lateral organization of bound STxB were analysed. The fatty acid of Gb3 significantly alters the ratio between the ordered and disordered phase and induces a third intermediate phase in the presence of unsaturated Gb3. The lateral organization of STxB on the membranes varies significantly. While STxB attached to membranes with Gb3s with saturated fatty acids forms protein clusters, it is more homogeneously bound to membranes containing unsaturated Gb3s. Large interphase lipid redistribution is observed for α-hydroxylated Gb3 doped membranes. Our results clearly demonstrate that the fatty acid of Gb3 strongly influences the lateral organization of STxB on the membrane and impacts the overall membrane organization of phase-separated lipid membranes.
志贺毒素B亚基(STxB)参与细胞膜附着和志贺毒素的转运,特异性地结合到糖神经酰胺Gb3上。在生物膜中,Gb3糖神经酰胺的脂肪酸组成不同,有强有力的证据表明脂肪酸改变STxB的结合行为以及志贺毒素/Gb3复合物的细胞内运输途径。为了分析STxB与不同Gb3的结合,我们化学合成了饱和、不饱和、α-羟基化的Gb3及其组合,所有这些都基于从单糖构建块、鞘氨醇和相应的脂肪酸开始的C24脂肪酸链。这些化学上定义明确的Gb3被插入到由DOPC/鞘磷脂/胆固醇组成的固相分离脂质双层中,作为动物细胞膜外叶的简单模拟物。通过荧光显微镜和原子力显微镜分析了双层的相行为以及STxB结合的侧向组织。Gb3的脂肪酸显著改变了有序和无序相的比例,并在存在不饱和Gb3的情况下诱导了第三种中间相。STxB在膜上的侧向组织显著变化。当STxB附着在含有饱和脂肪酸Gb3的膜上时形成蛋白质簇,它更均匀地结合到含有不饱和Gb3的膜上。观察到α-羟基化Gb3掺杂膜的大相间脂质重分布。我们的结果清楚地表明,Gb3的脂肪酸强烈影响STxB在膜上的侧向组织,并影响相分离脂质膜的整体膜组织。