Okada Kyoko, Ravi Harini, Smith Ellen M, Goode Bruce L
Department of Biology and Rosenstiel Basic Medical Science Research Center, Brandeis University, Waltham, MA 02454, USA.
Mol Biol Cell. 2006 Jul;17(7):2855-68. doi: 10.1091/mbc.e06-02-0135. Epub 2006 Apr 12.
Rapid turnover of actin structures is required for dynamic remodeling of the cytoskeleton and cell morphogenesis, but the mechanisms driving actin disassembly are poorly defined. Cofilin plays a central role in promoting actin turnover by severing/depolymerizing filaments. Here, we analyze the in vivo function of a ubiquitous actin-interacting protein, Aip1, suggested to work with cofilin. We provide the first demonstration that Aip1 promotes actin turnover in living cells. Further, we reveal an unanticipated role for Aip1 and cofilin in promoting rapid turnover of yeast actin cables, dynamic structures that are decorated and stabilized by tropomyosin. Through systematic mutagenesis of Aip1 surfaces, we identify two well-separated F-actin-binding sites, one of which contributes to actin filament binding and disassembly specifically in the presence of cofilin. We also observe a close correlation between mutations disrupting capping of severed filaments in vitro and reducing rates of actin turnover in vivo. We propose a model for balanced regulation of actin cable turnover, in which Aip1 and cofilin function together to "prune" tropomyosin-decorated cables along their lengths. Consistent with this model, deletion of AIP1 rescues the temperature-sensitive growth and loss of actin cable defects of tpm1Delta mutants.
肌动蛋白结构的快速周转对于细胞骨架的动态重塑和细胞形态发生是必需的，但驱动肌动蛋白解聚的机制仍不清楚。丝切蛋白通过切断/解聚细丝在促进肌动蛋白周转中起核心作用。在这里，我们分析了一种普遍存在的肌动蛋白相互作用蛋白Aip1在体内的功能，该蛋白被认为与丝切蛋白协同作用。我们首次证明Aip1促进活细胞中的肌动蛋白周转。此外，我们揭示了Aip1和丝切蛋白在促进酵母肌动蛋白电缆快速周转方面的意外作用，肌动蛋白电缆是由原肌球蛋白修饰和稳定的动态结构。通过对Aip1表面进行系统诱变，我们确定了两个相距较远的F-肌动蛋白结合位点，其中一个位点在丝切蛋白存在的情况下特异性地促进肌动蛋白丝的结合和解聚。我们还观察到，在体外破坏切断细丝封端的突变与体内降低肌动蛋白周转速率之间存在密切相关性。我们提出了一个肌动蛋白电缆周转平衡调节模型，其中Aip1和丝切蛋白共同作用，沿其长度“修剪”原肌球蛋白修饰的电缆。与该模型一致，删除AIP1可挽救tpm1Delta突变体的温度敏感生长和肌动蛋白电缆缺陷。
