Klejnot Marta, Gabrielsen Mads, Cameron Jenifer, Mleczak Andrzej, Talapatra Sandeep K, Kozielski Frank, Pannifer Andrew, Olson Michael F
Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Glasgow G61 1BD, Scotland.
Acta Crystallogr D Biol Crystallogr. 2013 Sep;69(Pt 9):1780-8. doi: 10.1107/S0907444913014418. Epub 2013 Aug 17.
The actin cytoskeleton is the chassis that gives a cell its shape and structure, and supplies the power for numerous dynamic processes including motility, endocytosis, intracellular transport and division. To perform these activities, the cytoskeleton undergoes constant remodelling and reorganization. One of the major actin-remodelling families are the cofilin proteins, made up of cofilin 1, cofilin 2 and actin-depolymerizing factor (ADF), which sever aged ADP-associated actin filaments to reduce filament length and provide new potential nucleation sites. Despite the significant interest in cofilin as a central node in actin-cytoskeleton dynamics, to date the only forms of cofilin for which crystal structures have been solved are from the yeast, Chromalveolata and plant kingdoms; none have previously been reported for an animal cofilin protein. Two distinct regions in animal cofilin are significantly larger than in the forms previously crystallized, suggesting that they would be uniquely organized. Therefore, it was sought to determine the structure of human cofilin 1 by X-ray crystallography to elucidate how it could interact with and regulate dynamic actin-cytoskeletal structures. Although wild-type human cofilin 1 proved to be recalcitrant, a C147A point mutant yielded crystals that diffracted to 2.8 Å resolution. These studies revealed how the actin-binding helix undergoes a conformational change that increases the number of potential hydrogen bonds available for substrate binding.
肌动蛋白细胞骨架是赋予细胞形状和结构的框架，并为包括运动、内吞作用、细胞内运输和分裂在内的众多动态过程提供动力。为了执行这些活动，细胞骨架会不断进行重塑和重组。肌动蛋白重塑的主要家族之一是丝切蛋白家族，由丝切蛋白1、丝切蛋白2和肌动蛋白解聚因子（ADF）组成，它们切断老化的与ADP相关的肌动蛋白丝，以缩短丝的长度并提供新的潜在成核位点。尽管丝切蛋白作为肌动蛋白细胞骨架动力学的核心节点备受关注，但迄今为止，已解析出晶体结构的丝切蛋白形式仅来自酵母、囊泡虫和植物界；此前尚未有动物丝切蛋白的晶体结构报道。动物丝切蛋白中有两个不同区域比之前结晶的形式明显更大，这表明它们的组织方式独特。因此，人们试图通过X射线晶体学确定人丝切蛋白1的结构，以阐明它如何与动态肌动蛋白细胞骨架结构相互作用并对其进行调节。尽管野生型人丝切蛋白1难以结晶，但一个C147A点突变体产生了衍射分辨率达2.8 Å的晶体。这些研究揭示了肌动蛋白结合螺旋如何发生构象变化，从而增加可用于底物结合的潜在氢键数量。
