Nam Kwangho, Pu Jingzhi, Karplus Martin
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 01238; Department of Chemistry and Computational Life Science Cluster, Umeå University, 901 87, Umeå, Sweden;
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 01238; Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis, Indianapolis, IN 46202; and
Proc Natl Acad Sci U S A. 2014 Dec 16;111(50):17851-6. doi: 10.1073/pnas.1419486111. Epub 2014 Dec 1.
The rotary motor enzyme FoF1-ATP synthase uses the proton-motive force across a membrane to synthesize ATP from ADP and Pi (H2PO4(-)) under cellular conditions that favor the hydrolysis reaction by a factor of 2 × 10(5). This remarkable ability to drive a reaction away from equilibrium by harnessing an external force differentiates it from an ordinary enzyme, which increases the rate of reaction without shifting the equilibrium. Hydrolysis takes place in the neighborhood of one conformation of the catalytic moiety F1-ATPase, whose structure is known from crystallography. By use of molecular dynamics simulations we trap a second structure, which is rotated by 40° from the catalytic dwell conformation and represents the state associated with ATP binding, in accord with single-molecule experiments. Using the two structures, we show why Pi is not released immediately after ATP hydrolysis, but only after a subsequent 120° rotation, in agreement with experiment. A concerted conformational change of the α3β3 crown is shown to induce the 40° rotation of the γ-subunit only when the βE subunit is empty, whereas with Pi bound, βE serves as a latch to prevent the rotation of γ. The present results provide a rationalization of how F1-ATPase achieves the coupling between the small changes in the active site of βDP and the 40° rotation of γ.
旋转马达酶F₀F₁ - ATP合酶利用跨膜质子动力势，在有利于水解反应（水解反应速率比合成反应快2×10⁵倍）的细胞条件下，从ADP和Pi（H₂PO₄⁻）合成ATP。这种通过利用外力驱动反应远离平衡的非凡能力，使其有别于普通酶，普通酶只是增加反应速率而不改变平衡。水解发生在催化部分F₁ - ATP酶的一种构象附近，其结构已由晶体学确定。通过分子动力学模拟，我们捕捉到了第二种结构，它相对于催化停留构象旋转了40°，代表与ATP结合相关的状态，这与单分子实验结果一致。利用这两种结构，我们证明了为什么Pi在ATP水解后不会立即释放，而是在随后120°旋转后才释放，这与实验结果相符。结果表明，只有当βE亚基为空时，α₃β₃冠的协同构象变化才会诱导γ亚基旋转40°，而当结合Pi时，βE起到闩锁作用以防止γ旋转。目前的结果为F₁ - ATP酶如何实现βDP活性位点的微小变化与γ亚基40°旋转之间的偶联提供了一种合理的解释。
