Structural basis of the specific protein-protein interactions underlying IF assem

如本PPG的概述部分所示，Vimentin由一个中央杆状结构域组成，两侧是非螺旋头和尾结构域。中心杆状结构域在非极残基的分布中显示出明显的七个残基周期(ABCDEFG)n。在这个重复序列中，a和d位置优先被Leu、Lie等小的非极性残基占据。Met或Val，通常用于所谓的盘绕线圈结构(1)。卷曲螺旋是由两个或多个相互缠绕在一起的a-螺旋形成的超螺旋，是蛋白质(2，3)中广泛存在的结构基序。这种常见的结构基序使IF蛋白能够在没有任何辅助蛋白质或因子的情况下在体外自组装成10 nm的细丝。这些细丝是绳状的组件 由2到6个4.5 nm的原纤维(即，每个包含8个IF多肽)制成，这些原纤维又由两个相互缠绕的3 nm的原丝(4，5)组成。虽然3 nm原丝的分子结构还没有被精确定义，但它似乎是由两个反平行的IF二聚体组成的，后者是两个平行的、登记在册的IF多肽的2链a螺旋卷曲(即，通过中心杆域形成)(也见图6)。

As indicated in the overview section of this PPG, vimentin consists of a central rod domain flanked by nona-helical head and tail domains. The central rod domain reveals a pronounced seven-residue periodicity, (abcdefg)n, in the distribution of apolar residues. Within this repeat, positions a and d are preferentially occupied by small apolar residues like Leu, lie. Met or Val, typical for a so-called coiled-coil structure (1). A coiled coil is formed by two or more a-helices wound around each other in a 'superhelix', and is a widespread structural motif in proteins (2, 3). This common structural motif enables IF proteins to self-assemble into 10-nm filaments in vitro In the absence of any auxiliary proteins or factors. These filaments are rope-like assemblies made from two to six 4.5-nm protofibrils (i.e., containing eight IF polypeptides each) which, in turn, are made of two intertwined 3-nm protofilaments each (4, 5). Although the molecular architecture of the 3-nm protofilament has not yet been precisely defined, it appears to be made from two antiparallel IF dimers, the latter being 2-stranded a-helical coiled-coils (i.e., formed via the central rod domain) of two parallel, in-register IF polypeptides (also see Figure 6).