Human mitochondrial ADP/ATP carrier SLC25A4 operates with a ping-pong kinetic mechanism.
Human mitochondrial ADP/ATP carrier SLC25A4 operates with a ping-pong kinetic mechanism.
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DOI：
10.15252/embr.202357127
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发表时间：
2023-08-03
期刊：
影响因子：
7.7
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中科院分区：
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线粒体ADP/ATP载体（SLC 25 A4），也称为腺嘌呤核苷酸移位酶，将ADP输入线粒体基质并输出ATP，这是氧化磷酸化的关键步骤。历史上，载体被认为形成同二聚体并通过顺序动力学机制操作，其涉及与同时结合的两个交换的底物形成三元复合物。然而，最近的结构和功能数据表明，线粒体ADP/ATP载体作为一个单体，并有一个单一的底物结合位点，这不能与顺序动力学机制相协调。在这里，我们研究了人类线粒体ADP/ATP载体的动力学特性，通过使用蛋白脂质体和运输机器人。我们表明，Km/Vmax的比例是恒定的所有测得的内部浓度。因此，与先前的声明相反，我们得出结论，载体以乒乓动力学机制运行，其中跨膜的底物交换连续发生而不是同时发生。这些数据结合了动力学和结构模型，表明载体以交替访问机制操作。人线粒体ADP/ATP载体（SLC 25 A4）以乒乓动力学机制运行，其中一种底物在另一种底物输出之前输入。
The mitochondrial ADP/ATP carrier (SLC25A4), also called the adenine nucleotide translocase, imports ADP into the mitochondrial matrix and exports ATP, which are key steps in oxidative phosphorylation. Historically, the carrier was thought to form a homodimer and to operate by a sequential kinetic mechanism, which involves the formation of a ternary complex with the two exchanged substrates bound simultaneously. However, recent structural and functional data have demonstrated that the mitochondrial ADP/ATP carrier works as a monomer and has a single substrate binding site, which cannot be reconciled with a sequential kinetic mechanism. Here, we study the kinetic properties of the human mitochondrial ADP/ATP carrier by using proteoliposomes and transport robotics. We show that the Km/Vmax ratio is constant for all of the measured internal concentrations. Thus, in contrast to earlier claims, we conclude that the carrier operates with a ping‐pong kinetic mechanism in which substrate exchange across the membrane occurs consecutively rather than simultaneously. These data unite the kinetic and structural models, showing that the carrier operates with an alternating access mechanism. The human mitochondrial ADP/ATP carrier (SLC25A4) operates with a ping‐pong kinetic mechanism in which one substrate is imported before the other substrate is exported.