The Center for Insoluble Protein Structures (inSPIN), Aarhus University, Aarhus, Denmark.
PLoS One. 2013 Jun 12;8(6):e63635. doi: 10.1371/journal.pone.0063635. Print 2013.
The competitive inhibitor cocaine and the non-competitive inhibitor ibogaine induce different conformational states of the human serotonin transporter. It has been shown from accessibility experiments that cocaine mainly induces an outward-facing conformation, while the non-competitive inhibitor ibogaine, and its active metabolite noribogaine, have been proposed to induce an inward-facing conformation of the human serotonin transporter similar to what has been observed for the endogenous substrate, serotonin. The ligand induced conformational changes within the human serotonin transporter caused by these three different types of ligands, substrate, non-competitive and competitive inhibitors, are studied from multiple atomistic molecular dynamics simulations initiated from a homology model of the human serotonin transporter. The results reveal that diverse conformations of the human serotonin transporter are captured from the molecular dynamics simulations depending on the type of the ligand bound. The inward-facing conformation of the human serotonin transporter is reached with noribogaine bound, and this state resembles a previously identified inward-facing conformation of the human serotonin transporter obtained from molecular dynamics simulation with bound substrate, but also a recently published inward-facing conformation of a bacterial homolog, the leucine transporter from Aquifex Aoelicus. The differences observed in ligand induced behavior are found to originate from different interaction patterns between the ligands and the protein. Such atomic-level understanding of how an inhibitor can dictate the conformational response of a transporter by ligand binding may be of great importance for future drug design.
竞争性抑制剂可卡因和非竞争性抑制剂伊博加因诱导人血清素转运蛋白呈现不同的构象状态。从可及性实验中可以看出，可卡因主要诱导外向构象，而非竞争性抑制剂伊博加因及其活性代谢物去甲伊博加因，据推测可诱导人血清素转运蛋白呈现类似于内源性底物血清素所观察到的内向构象。通过多种从人血清素转运蛋白同源模型出发的原子分子动力学模拟，研究了这三种不同类型的配体（底物、非竞争性抑制剂和竞争性抑制剂）诱导的人血清素转运蛋白内的配体诱导构象变化。结果表明，根据结合配体的类型，从分子动力学模拟中捕获到了人血清素转运蛋白的多种构象。与去甲伊博加因结合时，人血清素转运蛋白呈内向构象，这种状态类似于先前通过结合底物的分子动力学模拟获得的人血清素转运蛋白的一种已确定的内向构象，但也类似于最近发表的一种细菌同源物（来自 Aquifex Aoelicus 的亮氨酸转运蛋白）的内向构象。观察到的配体诱导行为的差异源自配体与蛋白质之间的不同相互作用模式。这种关于抑制剂如何通过配体结合来控制转运蛋白构象反应的原子水平理解，对于未来的药物设计可能具有重要意义。
