Three-dimensional structure of Wza, the protein required for translocation of group 1 capsular polysaccharide across the outer membrane of Escherichia coli
Three-dimensional structure of Wza, the protein required for translocation of group 1 capsular polysaccharide across the outer membrane of Escherichia coli
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DOI：
10.1074/jbc.m402913200
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发表时间：
2004-07-02
影响因子：
4.8
通讯作者：
Naismith, JH
中科院分区：
文献类型：
--
作者：
Beis, K;Collins, RF;Naismith, JH
Wza 是一种高度保守的多聚外膜蛋白复合物，是大肠杆菌中血清型 K30 1 组荚膜多糖表面表达所需的。在这里，我们展示了这种类型的多糖输出蛋白的第一个三维结构，分辨率为 15.5 埃，是使用冷冻阴性染色蛋白质数据集上的单粒子平均获得的。先前对纯化 Wza 的结构研究揭示了同源寡聚环结构，很可能由八个亚基组成。三维结构的对称分析结合生化二维和三维晶体学数据强烈表明Wza是具有C4准旋转对称性的八聚体复合物，并且被组织为二聚体亚基的四聚体。 Wza 最好的描述是两个直径不同的 4 埃高环的堆叠，从侧面看呈现蘑菇状外观。较大的戒指具有独特的方形形状，直径为 115 埃，而较小的戒指几乎呈圆形，直径为 90 埃。在复合体的中心，由四个对称臂包围的是一个直径约为 40 埃的小型椭圆形笼状空腔。中央空腔在复合体的顶部和底部被有效密封，但从侧面看时有小的臂间孔。我们讨论了该复合物的结构以及对细胞表面多糖表面易位的影响。
Wza is a highly conserved multimeric outer membrane protein complex required for the surface expression of the serotype K30 group 1 capsular polysaccharide in Escherichia coli. Here we present the first three-dimensional structure of this type of polysaccharide exporter at a 15.5-Angstrom resolution obtained using single particle averaging on a dataset of cryo-negatively stained protein. Previous structural studies on purified Wza have revealed a homo-oligomeric ring structure that is most probably composed of eight subunits. Symmetry analysis of the three-dimensional structure combined with biochemical two-and three-dimensional crystallographic data strongly suggest that Wza is an octameric complex with a C4 quasi-rotational symmetry and is organized as a tetramer of dimeric subunits. Wza is best described as a stack of two 4-Angstrom high rings with differing diameters providing a mushroom-like aspect from the side. The larger ring has a distinctive square shape with a diameter of 115 Angstrom, whereas the smaller is almost circular with a diameter of 90 Angstrom. In the center of the complex and enclosed by the four symmetrical arms is a small elliptical cagelike cavity of similar to 40 Angstrom in diameter. The central cavity is effectively sealed at the top and bottom of the complex but has small inter-arm holes when viewed from the side. We discuss the structure of this complex and implications in the surface translocation of cell-surface polysaccharide.