Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany.
Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, 44227, Dortmund, Germany.
Nat Commun. 2024 Sep 11;15(1):7969. doi: 10.1038/s41467-024-52251-3.
Actin filament turnover involves subunits binding to and dissociating from the filament ends, with the pointed end being the primary site of filament disassembly. Several molecules modulate filament turnover, but the underlying mechanisms remain incompletely understood. Here, we present three cryo-EM structures of the F-actin pointed end in the presence and absence of phalloidin or DNase I. The two terminal subunits at the undecorated pointed end adopt a twisted conformation. Phalloidin can still bind and bridge these subunits, inducing a conformational shift to a flattened, F-actin-like state. This explains how phalloidin prevents depolymerization at the pointed end. Interestingly, two DNase I molecules simultaneously bind to the phalloidin-stabilized pointed end. In the absence of phalloidin, DNase I binding would disrupt the terminal actin subunit packing, resulting in filament disassembly. Our findings uncover molecular principles of pointed end regulation and provide structural insights into the kinetic asymmetry between the actin filament ends.
肌动蛋白丝的周转率涉及亚基与丝的末端结合和解离，其中尖端是丝解聚的主要部位。有几种分子可以调节丝的周转率，但潜在的机制仍不完全清楚。在这里，我们展示了在有丝朊毒素或 DNase I 存在和不存在的情况下 F-肌动蛋白尖端的三个冷冻电镜结构。未修饰的尖端的两个末端亚基采用扭曲构象。丝朊毒素仍能结合并桥连这些亚基，诱导构象向扁平化的 F-肌动蛋白样状态转变。这解释了丝朊毒素如何防止尖端的解聚。有趣的是，两个 DNase I 分子同时结合到丝朊毒素稳定的尖端。在没有丝朊毒素的情况下，DNase I 的结合会破坏末端肌动蛋白亚基的组装，导致丝的解聚。我们的发现揭示了尖端调节的分子原理，并为肌动蛋白丝末端之间的动力学不对称性提供了结构见解。
