Class I myosins (myosin-Is) colocalize with Arp2/3 complex–nucleated actin networks at sites of membrane protrusion and invagination, but the mechanisms by which myosin-I motor activity coordinates with branched actin assembly to generate force are unknown. We mimicked the interplay of these proteins using the “comet tail” bead motility assay, where branched actin networks are nucleated by the Arp2/3 complex on the surface of beads coated with myosin-I and nucleation-promoting factor. We observed that myosin-I increased bead movement efficiency by thinning actin networks without affecting growth rates. Myosin-I triggered symmetry breaking and comet tail formation in dense networks resistant to spontaneous fracturing. Even with arrested actin assembly, myosin-I alone could break the network. Computational modeling recapitulated these observations, suggesting myosin-I acts as a repulsive force shaping the network’s architecture and boosting its force-generating capacity. We propose that myosin-I leverages its power stroke to amplify the forces generated by Arp2/3 complex–nucleated actin networks.

中文翻译：

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肌球蛋白-I 与 Arp2/3 复合物协同作用，以增强支链肌动蛋白网络的推动力


I 类肌球蛋白 （肌球蛋白-Is） 在膜突出和内陷部位与 Arp2/3 复合体有核肌动蛋白网络共定位，但肌球蛋白-I 运动活动与支链肌动蛋白组装协调以产生力的机制尚不清楚。我们使用“彗尾”珠子运动测定法模拟了这些蛋白质的相互作用，其中支链肌动蛋白网络被涂有肌球蛋白-I 和成核促进因子的珠子表面的 Arp2/3 复合物成核。我们观察到肌球蛋白-I 通过在不影响生长速率的情况下减薄肌动蛋白网络来提高珠子运动效率。肌球蛋白-I 在抵抗自发性破裂的致密网络中触发对称性破坏和彗尾形成。即使肌动蛋白组装停滞，肌球蛋白 I 本身也可以破坏网络。计算模型概括了这些观察结果，表明肌球蛋白 I 作为一种排斥力塑造了网络的架构并增强了其发力能力。我们提出肌球蛋白-I 利用其动力冲程来放大 Arp2/3 复合体有核肌动蛋白网络产生的力。