线粒体ATP合酶中的质子动力c环旋转对于将跨膜质子动力转化为扭矩以驱动三磷酸腺苷(ATP)的合成至关重要。利用最近的低温EM结构,我们的目标是对功能定向旋转如何实现的结构和能量理解。我们进行了多微秒原子模拟,以确定新质子到达前后沿c环旋转角的自由能分布。我们的结果表明,旋转是通过环在a亚基表面上的动态滑动而进行的,在此期间与保守的极性残基的相互作用稳定不同的中间体。有序的水链在这些中间体之一中排列成Grotthuss型质子转移。质子转移后,高屏障防止向后旋转,自由能的整体下降有利于向前旋转,确保热力学上不利的ATP合成所需的c环旋转的方向性。a亚基的必需精氨酸通过与c环的盐桥稳定旋转的构型。总的来说,我们描述了ATP合酶转子旋转步骤的完整机制,从而以原子分辨率照亮了对所有生命至关重要的过程。
Proton-powered c-ring rotation in mitochondrial ATP synthase is crucial to convert the transmembrane protonmotive force into torque to drive the synthesis of adenosine triphosphate (ATP). Capitalizing on recent cryo-EM structures, we aim at a structural and energetic understanding of how functional directional rotation is achieved. We performed multi-microsecond atomistic simulations to determine the free energy profiles along the c-ring rotation angle before and after the arrival of a new proton. Our results reveal that rotation proceeds by dynamic sliding of the ring over the a-subunit surface, during which interactions with conserved polar residues stabilize distinct intermediates. Ordered water chains line up for a Grotthuss-type proton transfer in one of these intermediates. After proton transfer, a high barrier prevents backward rotation and an overall drop in free energy favors forward rotation, ensuring the directionality of c-ring rotation required for the thermodynamically disfavored ATP synthesis. The essential arginine of the a-subunit stabilizes the rotated configuration through a salt bridge with the c-ring. Overall, we describe a complete mechanism for the rotation step of the ATP synthase rotor, thereby illuminating a process critical to all life at atomic resolution.