Uncoupling actin filament fragmentation by cofilin from increased subunit turnover.
Uncoupling actin filament fragmentation by cofilin from increased subunit turnover.
复制标题
DOI：
10.1006/jmbi.2000.3688
复制
发表时间：
2000-05
影响因子：
5.6
通讯作者：
B. Pope;S. Gonsior;S. Yeoh;A. McGough;A. Weeds
中科院分区：
文献类型：
--
作者：
B. Pope;S. Gonsior;S. Yeoh;A. McGough;A. Weeds
肌动蛋白解聚因子（ADF）/cofilin蛋白家族与肌动蛋白单体和细丝以pH敏感的方式相互作用。当ADF/cofilin结合F-肌动蛋白时，它诱导螺旋扭曲和断裂的变化;它还加速了亚基从细丝尖端的解离，从而增加了螺旋碾磨或解聚。使用定点突变，我们的特点是两个肌动蛋白结合位点的人cofilin。选择一个靶位点是因为我们先前表明绒毛蛋白头部片段与ADF竞争结合F-肌动蛋白。ADF/cofilin和肌动蛋白结合所必需的绒毛蛋白头部部分之间的有限序列同源性表明，cofilin上的肌动蛋白结合位点涉及在分子的相对端的结构环到已经涉及肌动蛋白结合的α-螺旋。通过α-螺旋的结合主要是单体肌动蛋白，而环区是专门参与长丝协会。我们的特点是每个网站的肌动蛋白结合特性独立于其他。在环区域中的单个赖氨酸残基的突变废除了与细丝的结合，但不废除与单体的结合。使用类似于cofilin（S3 D）的磷酸化形式的突变，我们表明，在生理离子强度下，但在低盐条件下，丝结合被抑制。在低离子强度下，该突变体诱导野生型cofilin的扭曲变化和片段化特征，但不激活亚基解离。结果表明，一个两个网站结合到细丝，通过环网站的协会发起，然后通过在分子的另一端的“螺旋”网站与相邻的亚基的相互作用。总之，这些相互作用诱导丝的扭曲和断裂，但扭曲变化本身并不负责肌动蛋白亚基从丝释放的速率增加。
The actin depolymerizing factor (ADF)/cofilin family of proteins interact with actin monomers and filaments in a pH-sensitive manner. When ADF/cofilin binds F-actin it induces a change in the helical twist and fragmentation; it also accelerates the dissociation of subunits from the pointed ends of filaments, thereby increasing treadmilling or depolymerization. Using site-directed mutagenesis we characterized the two actin-binding sites on human cofilin. One target site was chosen because we previously showed that the villin head piece competes with ADF for binding to F-actin. Limited sequence homology between ADF/cofilin and the part of the villin headpiece essential for actin binding suggested an actin-binding site on cofilin involving a structural loop at the opposite end of the molecule to the alpha-helix already implicated in actin binding. Binding through the alpha-helix is primarily to monomeric actin, whereas the loop region is specifically involved in filament association. We have characterized the actin binding properties of each site independently of the other. Mutation of a single lysine residue in the loop region abolishes binding to filaments, but not to monomers. Using the mutation analogous to the phosphorylated form of cofilin (S3D), we show that filament binding is inhibited at physiological ionic strength but not under low salt conditions. At low ionic strength, this mutant induces both the twist change and fragmentation characteristic of wild-type cofilin, but does not activate subunit dissociation. The results suggest a two-site binding to filaments, initiated by association through the loop site, followed by interaction with the adjacent subunit through the "helix" site at the opposite end of the molecule. Together, these interactions induce twist and fragmentation of filaments, but the twist change itself is not responsible for the enhanced rate of actin subunit release from filaments.