Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Mol Biol Cell. 2011 Oct;22(20):3826-39. doi: 10.1091/mbc.E11-06-0492. Epub 2011 Aug 24.
Fission yeast expresses three formins required for distinct actin cytoskeletal processes: Cdc12 (cytokinesis), For3 (polarization), and Fus1 (mating). We propose that in addition to differential regulation, key actin-assembly properties tailor formins for a particular role. In direct comparison to the well-studied Cdc12, we report the first in vitro characterization of the actin-assembly properties of For3 and Fus1. All three share fundamental formin activities; however, particular reaction rates vary significantly. Cdc12 is an efficient nucleator (one filament per approximately 3 Cdc12 dimers) that processively elongates profilin-actin at a moderate rate of 10 subunits s(-1) μM(-1), but lacks filament-bundling activity. Fus1 is also an efficient nucleator, yet processively elongates profilin-actin at one-half the rate of and dissociates 10-fold more rapidly than Cdc12; it also bundles filaments. For3 nucleates filaments 100-fold less well than Fus1, but like Cdc12, processively elongates profilin-actin at a moderate rate and lacks filament-bundling activity. Additionally, both the formin homology FH1 and FH2 domains contribute to the overall rate of profilin-actin elongation. We also confirmed the physiological importance of the actin-assembly activity of the fission yeast formins. Point mutants that disrupt their ability to stimulate actin assembly in vitro do not function properly in vivo.
裂殖酵母表达三种肌动蛋白细胞骨架过程所必需的formin：Cdc12（胞质分裂）、For3（极化）和 Fus1（交配）。我们提出，除了差异调节外，关键的肌动蛋白组装特性使formin 适用于特定的作用。与研究充分的 Cdc12 相比，我们首次报道了 For3 和 Fus1 的肌动蛋白组装特性的体外特征。所有这三种都具有基本的formin 活性；然而，特定的反应速率有很大的差异。Cdc12 是一种有效的成核剂（大约每 3 个 Cdc12 二聚体一个纤维），以中等速度 10 个亚基 s(-1) μM(-1) 连续延伸肌动蛋白-肌动蛋白结合蛋白，但缺乏纤维束形成活性。Fus1 也是一种有效的成核剂，但以一半的速度连续延伸肌动蛋白-肌动蛋白结合蛋白，解离速度比 Cdc12 快 10 倍；它还捆绑纤维。For3 的成核纤维的效率比 Fus1 低 100 倍，但与 Cdc12 一样，以中等速度连续延伸肌动蛋白-肌动蛋白结合蛋白，并且缺乏纤维束形成活性。此外，formin 同源 FH1 和 FH2 结构域都有助于肌动蛋白结合蛋白延伸的整体速率。我们还证实了裂殖酵母 formin 肌动蛋白组装活性的生理重要性。破坏其在体外刺激肌动蛋白组装能力的点突变体在体内不能正常发挥作用。
