Fucini P, Renner C, Herberhold C, Noegel A A, Holak T A
Max Planck Institute for Biochemistry, Martinsried, F.R.G.
Nat Struct Biol. 1997 Mar;4(3):223-30. doi: 10.1038/nsb0397-223.
The 120,000 M(r) gelation factor and alpha-actinin are among the most abundant F-actin cross-linking proteins in Dictyostelium discoideum. Both molecules are rod-shaped homodimers. Each monomer chain is comprised of an actin-binding domain and a rod domain. The rod domain of the gelation factor consists of six 100-residue repetitive segments with high internal homology. We have now determined the three-dimensional structure of segment 4 of the rod domain of the gelation factor from D. discoideum using NMR spectroscopy. The segment consists of seven beta-sheets arranged in an immunoglobulin-like (Ig) fold. This is completely different from the alpha-actinin rod domain which consists of four spectrin-like alpha-helical segments. The gelation factor is the first example of an Ig-fold found in an actin-binding protein. Two highly homologous actin-binding proteins from human with similar sequences to the gelation factor, filamin and a 280,000 M(r) actin-binding protein (ABP-280), share conserved residues that form the core of the gelation factor repetitive segment structure. Thus, the segment 4 structure should be common to this subfamily of the spectrin superfamily. The structure of segment 4 together with previously published electron microscopy data, provide an explanation for the dimerization of the whole gelation factor molecule.
120,000 M(r) 凝胶化因子和α-辅肌动蛋白是盘基网柄菌中最丰富的F-肌动蛋白交联蛋白。这两种分子都是杆状同型二聚体。每个单体链由一个肌动蛋白结合结构域和一个杆状结构域组成。凝胶化因子的杆状结构域由六个具有高度内部同源性的100个残基的重复片段组成。我们现在使用核磁共振光谱法确定了来自盘基网柄菌的凝胶化因子杆状结构域第4片段的三维结构。该片段由七个以免疫球蛋白样（Ig）折叠排列的β-折叠片组成。这与由四个血影蛋白样α-螺旋片段组成的α-辅肌动蛋白杆状结构域完全不同。凝胶化因子是在肌动蛋白结合蛋白中发现的Ig折叠的第一个例子。来自人类的两种与凝胶化因子序列相似的高度同源的肌动蛋白结合蛋白，细丝蛋白和280,000 M(r) 肌动蛋白结合蛋白（ABP-280），共享形成凝胶化因子重复片段结构核心的保守残基。因此，第4片段的结构应该是血影蛋白超家族这个亚家族所共有的。第4片段的结构与先前发表的电子显微镜数据一起，为整个凝胶化因子分子的二聚化提供了解释。
