Olofsson A, Kavéus U, Hacksell I, Thelestam M, Hebert H
Department of Medical Biophysics, Karolinska Institutet, Stockholm, Sweden.
J Mol Biol. 1990 Jul 5;214(1):299-306. doi: 10.1016/0022-2836(90)90162-f.
Interaction of the pore-forming protein alpha-toxin from Staphylococcus aureus with lipid components from platelet membranes induces crystal formation of the toxin oligomers. Structure analysis of crystalline areas in either sodium phosphotungstic acid or a sodium phosphotungstic acid/glucose mixture has been performed with electron microscopy and image processing. Ordered domains extending up to a few micrometers were observed, particularly after application of alpha-toxin to pre-formed lipid layers. The crystals, showing tetragonal symmetry, formed either separate two-dimensional sheets or three-dimensional piles of layers. The corresponding unit cell parameter of the single layer was a = b = 109.4 A (standard deviation 2.1 A, n = 21). Incubation of the toxin with intact membranes or extracted lipids as well as application of the lipid layer technique resulted in congruous crystalline properties. The projected averaged alpha-toxin oligomer shows cyclic symmetry with a stain-filled space in the centre. The bulk of the three-dimensional model consists of four asymmetric protein units forming a ring. In addition, a small domain covers the central cavity at the face of the protein opposite to the underlying lipid. The conditions under which the tetragonal arrays are formed on the lipid layers suggest that the alpha-toxin molecule is in a conformation binding to a hydrophobic surface rather than fully inserted into a lipid bilayer.
金黄色葡萄球菌的成孔蛋白α-毒素与血小板膜脂质成分的相互作用会诱导毒素寡聚体形成晶体。利用电子显微镜和图像处理技术，对磷钨酸钠或磷钨酸钠/葡萄糖混合物中的晶体区域进行了结构分析。观察到有序结构域延伸至几微米，特别是在将α-毒素应用于预先形成的脂质层后。这些晶体呈四方对称，形成单独的二维片层或三维层堆。单层的相应晶胞参数为a = b = 109.4 Å（标准差2.1 Å，n = 21）。毒素与完整膜或提取的脂质孵育以及应用脂质层技术均产生一致的晶体特性。投影平均α-毒素寡聚体呈环状对称，中心有一个充满染色剂的空间。三维模型的主体由四个不对称蛋白质单元形成一个环组成。此外，一个小结构域覆盖了蛋白质与下层脂质相对面的中心腔。在脂质层上形成四方阵列的条件表明，α-毒素分子处于与疏水表面结合的构象，而非完全插入脂质双层中。
