Cohen-Krausz S, Trachtenberg S
Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem, 91120, Israel.
J Struct Biol. 1998;122(3):267-82. doi: 10.1006/jsbi.1998.4001.
Flagellar filaments are highly conserved structures in terms of the underlying symmetry of the polymer, subunit domain organization of the flagellin monomer, amino acid composition and primary sequence at the N and C termini. Traditionally, filaments are classified as "plain" or "complex." In complex filaments, the helical lattice is perturbed in a pairwise manner such that the symmetry is reduced along the 6-start helical lines. Both plain (unperturbed) and complex (helically perturbed) components are helically symmetric and share a common lattice. The perturbation in Rhizobium lupini H13-3 results in a subunit composed of a dimer of flagellin. We have generated a approximately 13 A resolution three-dimensional density map of the complex filament of R. lupini H13-3 from low-dose images of negatively stained filaments. Compared to a previous map, which extended to only approximately 25 A resolution and which was generated from only five filaments containing six layer-lines each, the current map is a product of merging 139 data sets containing 66 layer-lines each. The higher resolution and improved signal-to-noise yield a detailed and interpretable density map. The density map is divided into four concentric rings. These amount to two dense cylinders interconnected by low density radial spokes and wrapped by a three-start external winding. The unperturbed component of the map is strikingly similar to the known plain filament maps and, in particular, to that of Caulobacter crescentus. The helically perturbed component contributes mainly to the filaments's exterior (domain D3) where it comprises the tips of the outer domains interconnecting, pairwise, along the 11-start protofilaments and, again, laterally along the 6-start lines forming vertical and horizontal loops. Strong intersubunit connectivity occurs in the D2 shell and in the inner shell which is dominated by 3-start densities. The contribution of the complex component to the radial spokes seems negligible. Copyright 1998 Academic Press.
就聚合物的基本对称性、鞭毛蛋白单体的亚基结构域组织、氨基酸组成以及N端和C端的一级序列而言，鞭毛丝是高度保守的结构。传统上，鞭毛丝被分为“普通型”或“复合型”。在复合型鞭毛丝中，螺旋晶格以成对方式受到干扰，使得沿六起始螺旋线的对称性降低。普通型（未受干扰）和复合型（螺旋受扰）组分都是螺旋对称的，并且共享一个共同的晶格。羽扇豆根瘤菌H13-3中的这种干扰导致一个由鞭毛蛋白二聚体组成的亚基。我们从负染鞭毛丝的低剂量图像中生成了羽扇豆根瘤菌H13-3复合型鞭毛丝的分辨率约为13埃的三维密度图。与之前仅扩展到约25埃分辨率且仅由五条各含六条层线的鞭毛丝生成的图谱相比，当前图谱是合并了139个各含66条层线的数据集的产物。更高的分辨率和改进的信噪比产生了一个详细且可解释的密度图。该密度图分为四个同心环。这些相当于两个由低密度径向辐条相互连接并被一个三起始外部绕组包裹的致密圆柱体。图谱的未受干扰组分与已知的普通型鞭毛丝图谱非常相似，特别是与新月柄杆菌的图谱相似。螺旋受扰组分主要对鞭毛丝的外部（结构域D3）有贡献，在那里它沿着11起始原纤维成对互连的外部结构域的尖端，并且再次沿着形成垂直和水平环的6起始线横向排列。在D2壳层和以内壳层为主的3起始密度区域中存在强亚基间连接。复合型组分对径向辐条的贡献似乎可以忽略不计。版权所有1998年学术出版社。
