Yokota Etsuo, Tominaga Motoki, Mabuchi Issei, Tsuji Yasunori, Staiger Christopher J, Oiwa Kazuhiro, Shimmen Teruo
Department of Life Science, Graduate School of Life Science, University of Hyogo, Harima Science Park City, Kamigoricho, Akogun, Japan.
Plant Cell Physiol. 2005 Oct;46(10):1690-703. doi: 10.1093/pcp/pci185. Epub 2005 Aug 13.
From germinating pollen of lily, two types of villins, P-115-ABP and P-135-ABP, have been identified biochemically. Ca(2+)-CaM-dependent actin-filament binding and bundling activities have been demonstrated for both villins previously. Here, we examined the effects of lily villins on the polymerization and depolymerization of actin. P-115-ABP and P-135-ABP present in a crude protein extract prepared from germinating pollen bound to a DNase I affinity column in a Ca(2+)-dependent manner. Purified P-135-ABP reduced the lag period that precedes actin filament polymerization from monomers in the presence of either Ca(2+) or Ca(2+)-CaM. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca(2+) and this complex acts as a nucleus for polymerization of actin filaments. However, the nucleation activity of P-135-ABP is probably not relevant in vivo because the assembly of G-actin saturated with profilin, a situation that mimics conditions found in pollen, was not accelerated in the presence of P-135-ABP. P-135-ABP also enhanced the depolymerization of actin filaments during dilution-mediated disassembly. Growth from filament barbed ends in the presence of Ca(2+)-CaM was also prevented, consistent with filament capping activity. These results suggested that lily villin is involved not only in the arrangement of actin filaments into bundles in the basal and shank region of the pollen tube, but also in regulating and modulating actin dynamics through its capping and depolymerization (or fragmentation) activities in the apical region of the pollen tube, where there is a relatively high concentration of Ca(2+).
从百合萌发的花粉中，通过生化方法鉴定出了两种类型的绒毛蛋白，即P - 115 - ABP和P - 135 - ABP。此前已证明这两种绒毛蛋白都具有Ca(2 +)-CaM依赖性肌动蛋白丝结合和捆绑活性。在此，我们研究了百合绒毛蛋白对肌动蛋白聚合和解聚的影响。从萌发花粉制备的粗蛋白提取物中存在的P - 115 - ABP和P - 135 - ABP以Ca(2 +)依赖性方式与脱氧核糖核酸酶I亲和柱结合。纯化的P - 135 - ABP在存在Ca(2 +)或Ca(2 +)-CaM的情况下，缩短了肌动蛋白丝从单体聚合之前的延迟期。这些结果表明，P - 135 - ABP在存在Ca(2 +)时可与G - 肌动蛋白形成复合物，并且该复合物作为肌动蛋白丝聚合的核。然而，P - 135 - ABP的成核活性在体内可能并不相关，因为在存在P - 135 - ABP的情况下，富含脯肌动蛋白的G - 肌动蛋白的组装并未加速，而富含脯肌动蛋白的情况模拟了花粉中的条件。P - 135 - ABP在稀释介导的解聚过程中也增强了肌动蛋白丝的解聚。在存在Ca(2 +)-CaM的情况下，从丝的带刺末端的生长也受到抑制，这与丝封端活性一致。这些结果表明，百合绒毛蛋白不仅参与花粉管基部和柄部区域肌动蛋白丝束的排列，还通过其在花粉管顶端区域（Ca(2 +)浓度相对较高）的封端和解聚（或断裂）活性来调节和调控肌动蛋白动力学。
