Analysis of highly ordered architecture of actin cytoskeleton in plant cells.

植物绒毛，P-115-ABP和P-135-ABP，包含在从百合花粉中制备的粗提物中。在钙离子存在的情况下结合到DNase I亲和柱上，并用EGTA从柱上解离和洗脱。纯化的P-135-ABP在Ca~(2+)和Gt~(2+)存在下加速了G-肌动蛋白的聚合。这些结果表明，P-135-ABP能与G-肌动蛋白在Ca~(2+)和Gt~(2+)存在下形成络合物，从而作为肌动蛋白微丝聚合的核或种子。此外，P-135-ABP在有Ca~(2+)和Gt~(2+)存在的情况下，使肌动蛋白微丝末端封端，并使微丝断裂或解聚。P-135-ABP已被证明能将肌动蛋白细丝排列成束。因此，与动物绒毛蛋白一样，P-135-ABP以钙依赖的方式对肌动蛋白发挥不同的作用。根据对P-115-ABP一级结构的分析，推测P-115-ABP也具有与P-135-ABP相似的活性。因此，花粉管中的植物绒毛蛋白负责在低浓度的小腿区域捆绑肌动蛋白细丝，而参与解聚或切断顶端区域的肌动蛋白细丝，那里的钙浓度相对较高。在小分子G-肌动蛋白结合蛋白Profilin存在下，未发现P-135-ABP对肌动蛋白聚合的促进作用。结果表明，在萌发的花粉中，几乎所有的G-肌动蛋白都与Profilin形成复合体，其浓度与肌动蛋白的浓度相近。因此，有理由认为植物绒毛蛋白的肌动蛋白核活性在花粉中没有发挥作用。有趣的是，绒毛蛋白不仅与肌动蛋白-细丝束共定位，而且还与某些被认为是质点的细胞器共存。因此，植物绒毛蛋白可能是影响细胞器在细胞内定位的因素之一。

Plant villins, P-115-ABP and P-135-ABP, containing in a crude extract prepared from lily pollen. bound to a DNase I affinity column in the presence of Ca^<2+>, and were dissociated and eluted from the column with EGTA. Purified P-135-ABP accelerated the polymerization of G-actin in the presence of Ca^<2+>. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca^<2+> and consequently acts as a nucleus or seed for polymerization of actin filaments. Furthermore, P-135-ABP caped an actin filament end, and severed or depolymerized filaments in the presence of Ca^<2+>. P-135-ABP has been shown to arrange actin filaments into bundles. Hence, like animal villin, P-135-ABP exerts various effects on actin in a Ca^<2+>-dependent manner. Based on an analysis of the primary structure of P-115-ABP, it is assumed that P-115-ABP also has similar activities to those of P-135-ABP. Hence, plant villin in pollen tubes is responsible for bundling actin filaments in shank region, where low concentrations of Ca^<2+> are present, while is involved in depolymerizing or severing actin filaments in apical regions, where relatively high concentrations of Ca^<2+> concentrations are present. In the presence of profilin, a low molecular weight G-actin binding protein, the acceleration of actin polymerization by P-135-ABP was not found. It is indicated that almost of G-actin form complex with profilin present at similar concentration to that of actin in the germinating pollen. Hence, it is reasonable to consider that actin-nucleation activity of plant villin is not exerted in pollen.Villin is widely distributed in plant cells, such as tobacco cultured cells BY-2. Interestingly, villin is co-localized with not only actin-filament bundles, but also certain organelles considered to be plastides. Therefore, it is possible that plant villin is one of factor responsible in the positioning of the organelles in cells.