Maciver S K, Pope B J, Whytock S, Weeds A G
Medical Research Council Laboratory of Molecular Biology, Cambridge, England.
Eur J Biochem. 1998 Sep 1;256(2):388-97. doi: 10.1046/j.1432-1327.1998.2560388.x.
Actin depolymerizing factor (ADF) from vertebrates and actophorin from Acanthamoeba castellanii are members of a protein family that bind monomeric and polymeric actin and have been shown by microscopy to sever filaments. Here, we compare the properties of recombinant human ADF and actophorin using rabbit muscle actin. ADF binds tenfold more strongly than actophorin to monomeric actin (G-actin)-ATP, and both bind co-operatively to F-actin. ADF decorates filaments below pH 7.3 and induces substantial depolymerization at higher pH values [Hawkins, M., Pope, B., Maciver, S. K. & Weeds, A. G. (1993) Human actin depolymerizing factor mediates a pH-sensitive destruction of actin filaments, Biochemistry 32, 9985-9993], but, at all pH values tested, actophorin binds to filaments in a similar manner to ADF at pH 6.5. Both proteins increase the depolymerization rate at the pointed ends of gelsolin-capped filaments, but the effect of ADF is more marked at pH 8.0. Both proteins accelerate the nucleating activity when mixed with filamentous actin (F-actin), but not with gelsolin-capped filaments, and they rapidly decrease the lengths of filaments as evidenced by electron microscopy. Both of these effects are best explained by a weak severing activity. Our results are discussed in relation to earlier models and to the structural changes observed when ADF binds F-actin [McGough, A., Pope, B., Chiu, W. & Weeds, A. (1997) Cofilin changes the twist of F-actin: implications for actin filament dynamics and cellular function, J. Cell Biol. 138, 771-781]. We also discuss the relevance of these observations to their possible roles in facilitating actin turnover in cells, thereby regulating filament dynamics in cell motility.
脊椎动物的肌动蛋白解聚因子（ADF）和卡氏棘阿米巴的肌动蛋白结合蛋白是一个蛋白质家族的成员，它们能结合单体和多聚肌动蛋白，并且通过显微镜观察已证实它们能切断肌动蛋白丝。在此，我们使用兔肌肉肌动蛋白比较重组人ADF和肌动蛋白结合蛋白的特性。ADF与单体肌动蛋白（G-肌动蛋白）-ATP的结合力比肌动蛋白结合蛋白强10倍，并且二者都能协同结合F-肌动蛋白。在pH 7.3以下，ADF能修饰肌动蛋白丝，在较高pH值时会诱导大量解聚[霍金斯，M.，波普，B.，麦西弗，S. K. & 威兹，A. G.（1993年）人肌动蛋白解聚因子介导肌动蛋白丝的pH敏感型破坏，《生物化学》32卷，9985 - 9993页]，但是，在所有测试的pH值下，肌动蛋白结合蛋白在pH 6.5时与肌动蛋白丝的结合方式与ADF相似。两种蛋白质都能增加凝溶胶蛋白封端的肌动蛋白丝尖端的解聚速率，但ADF在pH 8.0时的作用更显著。当与丝状肌动蛋白（F-肌动蛋白）混合时，两种蛋白质都能加速成核活性，但与凝溶胶蛋白封端的肌动蛋白丝混合时则不然，并且如电子显微镜所示，它们能迅速缩短肌动蛋白丝的长度。这两种效应最好用弱切断活性来解释。我们结合早期模型以及ADF结合F-肌动蛋白时观察到的结构变化[麦高夫，A.，波普，B.，邱，W. & 威兹，A.（1997年）丝切蛋白改变F-肌动蛋白的扭曲：对肌动蛋白丝动力学和细胞功能的影响，《细胞生物学杂志》138卷，771 - 781页]来讨论我们的结果。我们还讨论了这些观察结果与其在促进细胞中肌动蛋白周转从而调节细胞运动中肌动蛋白丝动力学的可能作用的相关性。
