MreB, the bacterial ancestor of eukaryotic actin, is responsible for shape in most rod-shaped bacteria. Despite belonging to the actin family, the relevance of nucleotide-driven polymerization dynamics for MreB function is unclear. Here, we provide insights into the effect of nucleotide state on membrane binding of Spiroplasma citri MreB5 (ScMreB5). Filaments of ScMreB5WT and an ATPase-deficient mutant, ScMreB5E134A, assemble independently of the nucleotide state. However, capture of the filament dynamics revealed that efficient filament formation and organization through lateral interactions are affected in ScMreB5E134A. Hence, the catalytic glutamate functions as a switch, (a) by sensing the ATP-bound state for filament assembly and (b) by assisting hydrolysis, thereby potentially triggering disassembly, as observed in other actins. Glu134 mutation and the bound nucleotide exhibit an allosteric effect on membrane binding, as observed from the differential liposome binding. We suggest that the conserved ATP-dependent polymerization and disassembly upon ATP hydrolysis among actins has been repurposed in MreBs for modulating filament organization on the membrane.

中文翻译：

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细菌肌动蛋白 MreB 的丝状组​​织取决于核苷酸状态

MreB 是真核肌动蛋白的细菌祖先，负责大多数杆状细菌的形状。尽管属于肌动蛋白家族，但核苷酸驱动的聚合动力学与 MreB 功能的相关性尚不清楚。在这里，我们深入了解了核苷酸状态对柑橘螺原体 MreB5 (ScMreB5) 膜结合的影响。ScMreB5WT 和 ATPase 缺陷突变体 ScMreB5E134A 的细丝独立于核苷酸状态进行组装。然而，对细丝动力学的捕获表明，ScMreB5E134A 中通过横向相互作用的有效细丝形成和组织受到影响。因此，催化谷氨酸起到开关的作用，(a) 通过感测丝组装的 ATP 结合状态，以及 (b) 通过协助水解，从而可能触发分解，如在其他肌动蛋白中观察到的那样。从差异脂质体结合观察到，Glu134 突变和结合的核苷酸对膜结合表现出变构效应。我们认为，肌动蛋白之间 ATP 水解时保守的 ATP 依赖性聚合和分解已在 MreB 中重新利用，用于调节膜上的丝组织。