PDF(Pubmed)
Abstract：
Intracellular actin networks assemble through the addition of ATP-actin subunits at the growing barbed ends of actin filaments. This is followed by \"aging\" of the filament via ATP hydrolysis and subsequent phosphate release. Aged ADP-actin subunits thus \"treadmill\" through the filament before being released back into the cytoplasmic monomer pool as a result of depolymerization at filament pointed ends. The necessity for aging before filament disassembly is reinforced by preferential binding of cofilin to aged ADP-actin subunits over newly-assembled ADP-Pi actin subunits in the filament. Consequently, investigations into how cofilin influences pointed-end depolymerization have, thus far, focused exclusively on aged ADP-actin filaments. Using microfluidics-assisted Total Internal Reflection Fluorescence (mf-TIRF) microscopy, we reveal that, similar to their effects on ADP filaments, cofilin and cyclase-associated protein (CAP) also promote pointed-end depolymerization of ADP-Pi filaments. Interestingly, the maximal rates of ADP-Pi filament depolymerization by CAP and cofilin together remain approximately 20-40 times lower than for ADP filaments. Further, we find that the promotion of ADP-Pi pointed-end depolymerization is conserved for all three mammalian cofilin isoforms. Taken together, the mechanisms presented here open the possibility of newly-assembled actin filaments being directly disassembled from their pointed-ends, thus bypassing the slow step of Pi release in the aging process.
摘要：
细胞内肌动蛋白网络通过在肌动蛋白丝的生长的倒钩末端添加ATP-肌动蛋白亚基来组装。随后是通过ATP水解和随后的磷酸盐释放的长丝的“老化”。老化的ADP-肌动蛋白亚基因此通过细丝“跑步机”，然后由于细丝尖端的解聚而释放回细胞质单体池。通过将丝线蛋白优先结合到细丝中新组装的ADP-Pi肌动蛋白亚基，可以增强在细丝拆卸之前进行老化的必要性。因此,对cofilin如何影响尖端解聚的研究，到目前为止，专注于老化的ADP-肌动蛋白丝。使用微流体辅助全内反射荧光（mf-TIRF）显微镜，我们透露，类似于它们对ADP细丝的影响，cofilin和环化酶相关蛋白（CAP）也促进ADP-Pi细丝的末端解聚。有趣的是,CAP和cofilin的ADP-Pi长丝解聚的最大速率比ADP长丝低约20-40倍。Further,我们发现，对于所有三种哺乳动物cofilin亚型，ADP-Pi末端解聚的促进都是保守的。一起来看,这里提出的机制打开了新组装的肌动蛋白丝直接从其尖端拆卸的可能性，从而绕过老化过程中Pi释放的缓慢步骤。
