Ludwig D S, Ribi H O, Schoolnik G K, Kornberg R D
Proc Natl Acad Sci U S A. 1986 Nov;83(22):8585-8. doi: 10.1073/pnas.83.22.8585.
The B subunit of cholera toxin forms two-dimensional crystals when bound to its membrane receptor, ganglioside GM1, in phospholipid layers. A rectangular crystal lattice gives diffraction extending to 15-A resolution in negative stain, and image-processing of electron micrographs reveals a ring of five protein densities. The diameter of the central hole and the outer diameter of the ring are about 20 and 60 A, respectively. These data are consistent with a pentameric, doughnut-shaped structure of the B subunit that lies flat on a membrane surface. A hexagonal crystal lattice is obtained as well, and results of image processing and chemical crosslinking allow two interpretations: the B subunit may exist in both pentameric and hexameric forms or, more likely, the hexagonal lattice may represent a disordered or liquid crystalline form, in which a pentamer undergoes rotational averaging about its 5-fold axis.
霍乱毒素的B亚基在磷脂层中与膜受体神经节苷脂GM1结合时会形成二维晶体。在负染条件下，矩形晶格衍射可延伸至15埃分辨率，对电子显微镜图像进行图像处理后发现有五个蛋白质密度组成的环。中心孔的直径和环的外径分别约为20埃和60埃。这些数据与B亚基呈五聚体、甜甜圈状结构且平躺在膜表面的情况相符。还获得了六边形晶格，图像处理和化学交联的结果有两种解释：B亚基可能以五聚体和六聚体两种形式存在，或者更有可能的是，六边形晶格可能代表一种无序或液晶形式，其中五聚体围绕其五重轴进行旋转平均。
