Mitochondrial ADP/ATP carriers import ADP into the mitochondrial matrix and export ATP to the cytosol to fuel cellular processes. Structures of the inhibited cytoplasmic- and matrix-open states have confirmed an alternating access transport mechanism, but the molecular details of substrate binding remain unresolved. Here, we evaluate the role of the solvent-exposed residues of the translocation pathway in the process of substrate binding. We identify the main binding site, comprising three positively charged and a set of aliphatic and aromatic residues, which bind ADP and ATP in both states. Additionally, there are two pairs of asparagine/arginine residues on opposite sides of this site that are involved in substrate binding in a state-dependent manner. Thus, the substrates are directed through a series of binding poses, inducing the conformational changes of the carrier that lead to their translocation. The properties of this site explain the electrogenic and reversible nature of adenine nucleotide transport.

线粒体 ADP/ATP 载体将 ADP 导入线粒体基质并将 ATP 导出到胞质溶胶，为细胞过程提供燃料。受抑制的细胞质和基质开放状态的结构证实了交替进入传输机制，但底物结合的分子细节仍未解决。在这里，我们评估了易位途径的溶剂暴露残基在底物结合过程中的作用。我们确定了主要的结合位点，包括三个带正电荷的和一组脂肪族和芳香族残基，它们在两种状态下都结合 ADP 和 ATP。此外，在该位点的两侧有两对天冬酰胺/精氨酸残基，它们以状态依赖的方式参与底物结合。因此，基板被引导通过一系列结合姿势，诱导导致其易位的载体构象变化。该位点的特性解释了腺嘌呤核苷酸转运的生电性和可逆性。