Mosser G, Mallouh V, Brisson A
Laboratoire de Génétique Moléculaire des Eucaryotes CNRS, Unité 184 de Biologie Moléculaire et de Génie Génétique INSERM, Institut de Chimie Biologique, Faculté de Médecine, Strasbourg, France.
J Mol Biol. 1992 Jul 5;226(1):23-8. doi: 10.1016/0022-2836(92)90120-9.
Highly ordered two-dimensional crystals of cholera toxin B-subunit pentamers have been grown by specific interaction with planar lipid films containing monosialoganglioside GM1. Electron diffractograms of frozen-hydrated crystals show diffraction peaks extending to beyond 4 A, while electron images diffract to 8 A. A two-dimensional projected structure of cholera toxin B-subunit-GM1 complex has been calculated at 9 A resolution by combining electron diffraction and image data. Crystals present an approximate pgg projection symmetry, with unit cell dimensions a = 119(+/- 1) A, b = 123(+/- 1) A, gamma = 90 degrees. Each pentameric assembly presents two concentric rings of electron scattering density, separated by an area of lower density. The outer and inner rings are centered at 25 A and and 11 A from the pentamer centre, respectively. The apparent projected density of the outer ring is larger than that of the inner ring. We propose that the outer and inner density rings correspond respectively to the peripheral beta-sheet arrangement and the central alpha-helix barrel, recently identified in the crystal structure of the heat-labile enterotoxin from Escherichia coli.
霍乱毒素B亚基五聚体的高度有序二维晶体，通过与含有单唾液酸神经节苷脂GM1的平面脂质膜特异性相互作用而生长。冷冻水合晶体的电子衍射图显示衍射峰延伸至4埃以外，而电子图像的衍射可达8埃。通过结合电子衍射和图像数据，已计算出霍乱毒素B亚基-GM1复合物在9埃分辨率下的二维投影结构。晶体呈现近似pgg投影对称性，晶胞尺寸a = 119（±1）埃，b = 123（±1）埃，γ = 90度。每个五聚体组装体呈现两个同心的电子散射密度环，由一个较低密度区域隔开。外环和内环分别以距五聚体中心25埃和11埃为中心。外环的表观投影密度大于内环。我们提出，外环和内环密度分别对应于最近在大肠杆菌不耐热肠毒素晶体结构中确定的外周β-折叠排列和中央α-螺旋桶。
