Dube P, Tavares P, Lurz R, van Heel M
Fritz Haber Institut der Max Planck Gesellschaft, Berlin, Germany.
EMBO J. 1993 Apr;12(4):1303-9. doi: 10.1002/j.1460-2075.1993.tb05775.x.
Electron microscopy in combination with image processing is a powerful method for obtaining structural information on non-crystallized biological macromolecules at the 10-50 A resolution level. The processing of noisy microscopical images requires advanced data processing methodologies in which one must carefully avoid the introduction of any form of bias into the data set. Using a novel multivariate statistical approach to the analysis of symmetry, we studied the structure of the bacteriophage SPP1 portal protein oligomer. This portal structure, ubiquitous in icosahedral bacteriophages which package dsDNA, is located at the site of symmetry mismatch between a 5-fold vertex of the icosahedral shell and the 6-fold symmetric (helical) tail. From previous studies such 'head-to-tail connector' structures were generally accepted to be homododecamers assembled in a 12-fold symmetric ring around a central channel. Using a new analysis methodology we have found that the phage SPP1 portal structure exhibits 13-fold cyclical symmetry: a new point group organization for oligomeric proteins. A model for the DNA packaging mechanism by 13-fold symmetric portal protein assemblies is presented which attributes a coherent functional meaning to their unusual symmetry.
电子显微镜与图像处理相结合是一种强大的方法，可在10 - 50埃分辨率水平上获取非结晶生物大分子的结构信息。处理有噪声的显微镜图像需要先进的数据处理方法，在这种方法中必须小心避免将任何形式的偏差引入数据集。我们使用一种新颖的多变量统计方法来分析对称性，研究了噬菌体SPP1门户蛋白寡聚体的结构。这种门户结构在包装双链DNA的二十面体噬菌体中普遍存在，位于二十面体外壳的五重顶点与六重对称（螺旋）尾部之间的对称不匹配位点。从先前的研究来看，这种“头对尾连接体”结构通常被认为是围绕中央通道以十二重对称环组装的同型十二聚体。使用一种新的分析方法，我们发现噬菌体SPP1门户结构呈现出十三重循环对称性：这是寡聚蛋白的一种新的点群组织形式。本文提出了一种由十三重对称门户蛋白组装体进行DNA包装机制的模型，该模型赋予了它们不寻常对称性连贯的功能意义。
