美国洛克菲勒大学Gregory M. Alushin团队近期取得重要工作进展，他们研究发现弯曲力和核苷酸状态共同调节F-肌动蛋白（F-actin）结构。该研究工作2022年10月26日在线发表于《自然》杂志上。

研究人员发现肌动蛋白的核苷酸状态调节由弯曲力诱发的F-肌动蛋白结构转换。ADP-F-actin和ADP-P_i-F-actin的冷冻电镜结构具有足够的分辨率，可以看到结合的溶剂，揭示了由水分子桥接的基体内界面，可以介导丝晶格的灵活性。尽管在核苷酸裂隙中存在广泛的有序溶剂差异，但这些结构具有几乎相同的晶格和基本上没有区别的蛋白质骨架构象，不太可能被肌动蛋白结合蛋白所区分。研究人员介绍了一个机器学习的方法，用于重建弯曲的细丝，使他们能够直观地看到连续的结构变化和侧链级的细节。弯曲的F-actin结构显示了在亚单位内部界面的重新排列，其特点是螺旋扭曲和单个原基的变形发生了实质性的改变，这种转变在ADP-F-actin和ADP-P_i-F-actin中是不同的。

这表明，磷酸盐使肌动蛋白亚单位僵化，从而改变了F-actin的弯曲结构。由于弯曲力唤起的核苷酸状态依赖性构象转变的幅度，足以被肌动蛋白结合蛋白检测到，研究人员提出，肌动蛋白核苷酸状态可以作为F-actin机械调节的共同调节因子。

据介绍，ATP-水解耦合的肌动蛋白聚合是细胞力产生的一个基本机制。反过来，力和肌动蛋白丝（F-actin）的核苷酸状态，通过调整F-actin与肌动蛋白结合蛋白的接触来调节肌动蛋白的动态，其机制尚不清楚。

附：英文原文

Title: Bending forces and nucleotide state jointly regulate F-actin structure

Author: Reynolds, Matthew J., Hachicho, Carla, Carl, Ayala G., Gong, Rui, Alushin, Gregory M.

Issue&Volume: 2022-10-26

Abstract: ATP-hydrolysis-coupled actin polymerization is a fundamental mechanism of cellular force generation1,2,3. In turn, force4,5 and actin filament (F-actin) nucleotide state6 regulate actin dynamics by tuning F-actin’s engagement of actin-binding proteins through mechanisms that are unclear. Here we show that the nucleotide state of actin modulates F-actin structural transitions evoked by bending forces. Cryo-electron microscopy structures of ADP–F-actin and ADP-Pi–F-actin with sufficient resolution to visualize bound solvent reveal intersubunit interfaces bridged by water molecules that could mediate filament lattice flexibility. Despite extensive ordered solvent differences in the nucleotide cleft, these structures feature nearly identical lattices and essentially indistinguishable protein backbone conformations that are unlikely to be discriminable by actin-binding proteins. We next introduce a machine-learning-enabled pipeline for reconstructing bent filaments, enabling us to visualize both continuous structural variability and side-chain-level detail. Bent F-actin structures reveal rearrangements at intersubunit interfaces characterized by substantial alterations of helical twist and deformations in individual protomers, transitions that are distinct in ADP–F-actin and ADP-Pi–F-actin. This suggests that phosphate rigidifies actin subunits to alter the bending structural landscape of F-actin. As bending forces evoke nucleotide-state dependent conformational transitions of sufficient magnitude to be detected by actin-binding proteins, we propose that actin nucleotide state can serve as a co-regulator of F-actin mechanical regulation.

DOI: 10.1038/s41586-022-05366-w

Source: https://www.nature.com/articles/s41586-022-05366-w