Arabidopsis VILLIN1 generates actin filament cables that are resistant to depolymerization
Arabidopsis VILLIN1 generates actin filament cables that are resistant to depolymerization
复制标题
DOI：
10.1105/tpc.104.028555
复制
发表时间：
2005-02-01
期刊：
影响因子：
11.6
通讯作者：
Staiger, CJ
中科院分区：
文献类型：
--
作者：
Huang, S;Robinson, RC;Staiger, CJ
动态的细胞质流动、细胞器定位和核迁移使用由肌动蛋白细丝排列成高阶结构(如肌动蛋白缆线和肌动蛋白束)产生的分子轨迹。这些阵列是如何形成和稳定的，以对抗细胞解聚力，仍然是一个悬而未决的问题。绒毛蛋白和纤毛蛋白是植物中最具特性的肌动蛋白-细丝束或交联蛋白，它们都是由拟南芥中的五个成员组成的多基因家族编码的。相关的绒毛蛋白和明胶蛋白是由六个同源的明胶蛋白结构域组成的核心的保守蛋白质。明胶蛋白是一种钙调节的肌动蛋白细丝切断、成核和带刺末端封顶因子。绒毛蛋白在其C端有第七个结构域，即绒毛蛋白头饰，它可以与肌动蛋白细丝结合，从而赋予交联剂或捆绑肌动蛋白细丝的能力。许多绒毛，但不是所有的，都保留了切断、核化和覆盖细丝的能力。在这里，我们通过比较人类明胶蛋白和植物绒毛蛋白与脊椎动物明胶蛋白的X射线结晶学数据的序列比对，确定了一种推测的钙不敏感的绒毛蛋白亚型。VILLIN1(VLN1)是拟南芥绒毛蛋白亚型中保守程度最低的钙结合位点。重组VLN1以高亲和力与肌动蛋白细丝结合(K-d类似于1微米)，并产生束状细丝网络；这两种性质都与游离钙离子浓度无关。与人血浆明胶蛋白不同，VLN1不会使单体中的细丝组装成核，不会阻止Profilin-Actin在带刺末端的聚合，也不会刺激解聚或切断原有的细丝。在ADF/Cofilin的动力学分析中，绒毛蛋白似乎首先与生长中的细丝结合，并保护细丝免受ADF介导的解聚。我们认为，VLN1是植物细胞中肌动蛋白细丝束的形成和稳定性的主要调节因子，即使在导致其他肌动蛋白阵列解聚的刺激存在的情况下，它也具有维持电缆网络的功能。
Dynamic cytoplasmic streaming, organelle positioning, and nuclear migration use molecular tracks generated from actin filaments arrayed into higher-order structures like actin cables and bundles. How these arrays are formed and stabilized, against cellular depolymerizing forces remains an open question. Villin and fimbrin are the best characterized actin-filament bundling or cross-linking proteins in plants and each is encoded by a multigene family of five members in Arabidopsis thaliana. The related villins and gelsolins are conserved proteins that are constructed from a core of six homologous gelsolin domains. Gelsolin is a calcium-regulated actin filament severing, nucleating and barbed end capping factor. Villin has a seventh domain at its C terminus, the villin headpiece, which can bind to an actin filament, conferring the ability to crosslink or bundle actin filaments. Many, but not all, villins retain the ability to sever, nucleate, and cap filaments. Here we have identified a putative calcium-insensitive villin isoform through comparison of sequence alignments between human gelsolin and plant villins with x-ray crystallography data for vertebrate gelsolin. VILLIN1 (VLN1) has the least well-conserved type 1 and type 2 calcium binding sites among the Arabidopsis VILLIN isoforms. Recombinant VLN1 binds to actin filaments with high affinity (K-d similar to1 muM) and generates bundled filament networks; both properties are independent of the free Ca2+ concentration. Unlike human plasma gelsolin, VLN1 does not nucleate the assembly of filaments from monomer, does not block the polymerization of profilin-actin onto barbed ends, and does not stimulate depolymerization or sever preexisting filaments. In kinetic assays with ADF/cofilin, villin appears to bind first to growing filaments and protects filaments against ADF-mediated depolymerization. We propose that VLN1 is a major regulator of the formation and stability of actin filament bundles in plant cells and that it functions to maintain the cable network even in the presence of stimuli that result in depolymerization of other actin arrays.