Inouye H, Tsuruta H, Sedzik J, Uyemura K, Kirschner D A
Department of Biology, Boston College, Chestnut Hill, Massachusetts 02467
Biophys J. 1999 Jan;76(1 Pt 1):423-37. doi: 10.1016/S0006-3495(99)77209-7.
Highly purified myelin P0 glycoprotein was solubilized to 1-8 mg/ml in 0.1% sodium dodecyl sulfate (SDS), and the solution structure of the P0 assembly was studied using synchrotron x-ray scattering. The full-length P0, which was isolated from bovine intradural roots, included both the extracellular and cytoplasmic domains of the molecule. At the higher concentrations (4, 6, and 8 mg/ml, respectively), an x-ray intensity maximum was observed at 316 A, 245 A, and 240 A Bragg spacing. Because the position of this intensity depended on P0 concentration, it is most likely due to interparticle interference. By contrast, the position of a second intensity maximum, which was at approximately 40 A Bragg spacing, was invariant with P0 concentration. This latter intensity was accounted for by monodispersed, 80 A-diameter particles that are composed of eight, approximately 30 A-diameter spheres. Chemical parameters suggest that the 80 A particles correspond to the size of a tetramer of P0 molecules. Therefore, the approximately 30 A spheres would correspond to the sizes of the extracellular and cytoplasmic domains for each of the P0 monomers. The invariance of the second intensity maximum with P0 concentration indicates that the structure of the 80 A-diameter, tetrameric particles is unaltered. According to the liquid model for interparticle interference from charged spheres, the 80 A-diameter particle has 10 negative surface charges which likely arise from negatively charged SDS molecules bound to the transmembrane domain of P0. This binding, however, apparently does not alter the tetrameric assembly of P0, suggesting that intermolecular interactions involving extracellular domains and cytoplasmic domains likely stabilize this assembly. Some of our results have been published in abstract form (Inouye, H., H. Tsuruta, D. A. Kirschner, J. Sedzik, and K. Uyemura. Abstracts of the 4th International School and Symposium on Synchrotron Radiation in Natural Science, June 15-20, 1998. Ustron-Jaszowiec, Poland. p. 31).
将高度纯化的髓磷脂P0糖蛋白在0.1%十二烷基硫酸钠（SDS）中溶解至1 - 8 mg/ml，并使用同步加速器X射线散射研究P0组装体的溶液结构。从牛硬膜内神经根分离得到的全长P0包含该分子的细胞外结构域和细胞质结构域。在较高浓度（分别为4、6和8 mg/ml）下，在316 Å、245 Å和240 Å的布拉格间距处观察到X射线强度最大值。由于该强度的位置取决于P0浓度，很可能是由于颗粒间干涉。相比之下，第二个强度最大值的位置在约40 Å布拉格间距处，不随P0浓度变化。后一种强度是由直径80 Å的单分散颗粒引起的，这些颗粒由八个直径约30 Å的球体组成。化学参数表明，80 Å的颗粒对应于P0分子四聚体的大小。因此，约30 Å的球体将对应于每个P0单体的细胞外结构域和细胞质结构域的大小。第二个强度最大值不随P0浓度变化表明，直径80 Å的四聚体颗粒的结构未改变。根据带电球体颗粒间干涉的液体模型，直径80 Å的颗粒有10个负表面电荷，这可能源于与P0跨膜结构域结合的带负电的SDS分子。然而，这种结合显然不会改变P0的四聚体组装，这表明涉及细胞外结构域和细胞质结构域的分子间相互作用可能稳定了这种组装。我们的一些结果已以摘要形式发表（Inouye, H., H. Tsuruta, D. A. Kirschner, J. Sedzik, and K. Uyemura. Abstracts of the 4th International School and Symposium on Synchrotron Radiation in Natural Science, June 15 - 20, 1998. Ustron - Jaszowiec, Poland. p. 31）。
