The role of the FH1 domain and profilin in formin-mediated actin-filament elongation and nucleation
The role of the FH1 domain and profilin in formin-mediated actin-filament elongation and nucleation
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DOI：
10.1016/j.cub.2007.11.062
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发表时间：
2008-01-08
期刊：
影响因子：
9.2
通讯作者：
Pollard, Thomas
中科院分区：
文献类型：
--
作者：
Paul, Aditya;Pollard, Thomas
背景：形成蛋白质使肌动蛋白丝从头成核，并与生长的倒刺末端保持联系。而formin同源性（FH）2域介导的进行性协会，FH 1域与肌动蛋白单体结合蛋白profilin的音乐会，增加了倒钩末端伸长的速度。实现这种效果的机制还不清楚。结果如下：我们使用全内反射荧光显微镜来测量profilin对与FH 1和FH 2构建体（来自S.酿酒酵母），其具有含有1至8个profilin结合聚脯氨酸轨道的FH 1结构域。在一个大的范围内的profilin浓度（0.5-25 μ M），有刺末端伸长的速度增加与在FH 1域中的聚脯氨酸轨道的数量。在FH 1介导的肌动蛋白亚基转移到倒刺末端的过程中，前纤维蛋白肌动蛋白与FH 1结构域的结合是限速步骤（速率至少为88 s（-1））。从在profilin存在下生长的倒刺末端的formins的解离与延伸率成比例。Profilin深刻地抑制成核的FH 2和FH 1 FH 2结构，但profilin-actin绑定到FH 1可能有助于弱成核。结论：为了实现快速延伸，FH 1结构域结合profilin-actin复合物，并将其快速递送至与FH 2结构域相关的倒刺末端。由于亚基添加促进FH 2结构域从生长的倒刺末端解离，因此FH 2结构域必须通过在肌动蛋白亚基添加偶联到肌动蛋白易位的每个循环期间易于解离的状态。
Background: Formin proteins nucleate actin filaments de novo and stay associated with the growing barbed end. Whereas the formin-homology (FH) 2 domains mediate processive association, the FH1 domains-in concert with the actin-monomer-binding protein profilin-increase the rate of barbed-end elongation. The mechanism by which this effect is achieved is not well understood. Results: We used total internal reflection fluorescence microscopy to measure the effect of profilin on the elongation of single actin filaments associated with FH1 FH2 constructs (derived from the formin Bni1 p from S. cerevisiae) with FH1 domains containing one to eight profilin-binding polyproline tracks. Over a large range of profilin concentrations (0.5-25 mu M), the rate of barbed-end elongation increases with the number of polyproline tracks in the FH1 domain. The binding of profilin-actin to the FH1 domain is the rate-limiting step (up to rates of at least 88 s(-1)) in FH1-mediated transfer of actin subunits to the barbed end. Dissociation of formins from barbed ends growing in the presence of profilin is proportional to the elongation rate. Profilin profoundly inhibits nucleation by FH2 and FH1 FH2 constructs, but profilin-actin bound to FH1 might contribute weakly to nucleation. Conclusions: To achieve fast elongation, formin FH1 domains bind profilin-actin complexes and deliver them rapidly to the barbed end associated with the FH2 domain. Because subunit addition promotes dissociation of FH2 domains from growing barbed ends, FH2 domains must pass through a state that is prone to dissociation during each cycle of actin subunit addition coupled to formin translocation.