MOLECULAR MODEL OF AN ACTIN FILAMENT CAPPED BY SEVERING PROTEIN, GELSOLIN

凝溶胶蛋白（Gelsolin）是一个由六个结构域（82 kDa）组成的蛋白质， 通过切断、封盖和成核长丝进行组装。 我们有 对修饰有G2 - 6的F-肌动蛋白进行了电子冷冻显微镜检查， 缺乏高亲和力单体结合的凝溶胶蛋白缺失突变体 这是高效切割所需的域。 电子 在钙中用G2 - 6修饰的F-肌动蛋白的冷冻显微照片，但在钙中没有。 EGTA是一种表现出正常切断活动的病症， 细丝的戏剧性扭曲似乎与 切断活动。 G2 - 6：F-actin的三维重建 是在允许切断的条件下获得的，但在较低的温度下， 效率 结构显示凝溶胶蛋白桥连两个 当它与纤维结合时，它会与纤维上的单体结合。 的 F-肌动蛋白结合位点轴向居中于亚结构域3，径向居中于亚结构域3。 位于上部肌动蛋白单体的亚结构域1和3之间。 两者 装饰细丝的扭曲外观和 G2 - 6密度表明，为了使结构域G4结合肌动蛋白， 切断细丝，凝溶胶蛋白和肌动蛋白都经历了大的 构象变化

Gelsolin is a six domain protein (82 kDa) which regulates actin assembly by severing, capping, and nucleating filaments. We have performed electron cryomicroscopy of F-actin decorated with G2-6, a gelsolin deletion mutant which lacks the high affinity monomer binding domain that is required for efficient severing. Electron cryomicrographs of F-actin decorated with G2-6 in calcium, but not in EGTA, a condition that exhibits normal severing activity, show dramatic distortions of filaments which appear to correlate with severing activity. A three-dimensional reconstruction of G2-6:F-actin was obtained under conditions which permit severing, but at a lower efficiency. The structure shows that gelsolin bridges two longitudinally-associated monomers when it binds the filament. The F-actin binding site is centered axially at subdomain 3 and radially between subdomains 1 and 3 of the upper actin monomer. Both the distorted appearance of the decorated filaments and the location of the G2-6 density suggest that in order for domain G4 to bind actin and sever the filament, both gelsolin and actin undergo large conformational changes.