Moore M D, DiScipio R G, Cooper N R, Nemerow G R
Department of Immunology, Research Institute of Scripps Clinic, La Jolla, California 92037.
J Biol Chem. 1989 Dec 5;264(34):20576-82.
The interaction of the Epstein-Barr virus/45-kDa proteolytic fragment of C3 (C3dg) receptor (CR2) with its viral ligand, the Epstein-Barr virus glycoprotein gp350/220, initiates the sequence of events leading to virus internalization and B lymphocyte transformation. Soluble recombinant receptor (rCR2) and gp350/220 as well as the natural ligand, C3dg, were subjected to a number of analytical techniques including gel permeation chromatography, density gradient ultracentrifugation, circular dichroism, and electron microscopy in order to determine their hydrodynamic, structural, and binding properties. Both rCR2 and gp350/220 were found to be highly extended proteins (f/fo = 2.1 and 2.4/2.2, respectively). C3dg, in contrast to the viral ligand, is only somewhat elongated (f/fo = 1.5). Soluble rCR2, visualized by high resolution electron microscopy, was shown to be an extended, highly flexible molecule comprised of ringlet domains, each approximately 24.1 A in length, which likely correspond to the short consensus repeat motif deduced from the CR2 cDNA nucleotide sequence. Ligand-binding studies carried out under physiological conditions indicated that gp350/220 binding to rCR2 was saturable and univalent, with a dissociation constant of 3.2 nM. In contrast, monomeric C3dg did not bind to rCR2 under physiological conditions; however, at reduced ionic strength, monomeric C3dg binding could be measured. These studies indicate that the affinity of the C3dg monomer for rCR2 under physiologic conditions is approximately 10(4)-fold less than that of the viral ligand. The molecular properties of rCR2 revealed in these studies provide essential information for future studies of the biologic functions of the Epstein-Barr virus/C3dg receptor.
爱泼斯坦-巴尔病毒/补体C3 45-kDa蛋白水解片段（C3dg）受体（CR2）与其病毒配体——爱泼斯坦-巴尔病毒糖蛋白gp350/220之间的相互作用，引发了一系列导致病毒内化和B淋巴细胞转化的事件。可溶性重组受体（rCR2）、gp350/220以及天然配体C3dg接受了多种分析技术检测，包括凝胶渗透色谱法、密度梯度超速离心法、圆二色性分析和电子显微镜检查，以确定它们的流体动力学、结构和结合特性。结果发现，rCR2和gp350/220均为高度伸展的蛋白质（f/fo分别为2.1和2.4/2.2）。相比之下，病毒配体C3dg只是略有拉长（f/fo = 1.5）。通过高分辨率电子显微镜观察到，可溶性rCR2是一个由小环结构域组成的伸展且高度灵活的分子，每个小环结构域长度约为24.1 Å，这可能与从CR2 cDNA核苷酸序列推导得出的短共有重复基序相对应。在生理条件下进行的配体结合研究表明，gp350/220与rCR2的结合具有饱和性和单价性，解离常数为3.2 nM。相反，在生理条件下，单体C3dg不与rCR2结合；然而，在离子强度降低时，可以检测到单体C3dg的结合。这些研究表明，在生理条件下，C3dg单体对rCR2的亲和力比病毒配体低约10^4倍。这些研究中揭示的rCR2的分子特性为未来研究爱泼斯坦-巴尔病毒/C3dg受体的生物学功能提供了重要信息。
