Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, NY 10065, USA.
Institute for Computational Biomedicine, Weill Medical College of Cornell University, New York, NY 10065, USA.
Sci Rep. 2017 Jan 6;7:40076. doi: 10.1038/srep40076.
The dopamine transporter (DAT) belongs to the neurotransmitter:sodium symporter (NSS) family of membrane proteins that are responsible for reuptake of neurotransmitters from the synaptic cleft to terminate a neuronal signal and enable subsequent neurotransmitter release from the presynaptic neuron. The release of one sodium ion from the crystallographically determined sodium binding site Na2 had been identified as an initial step in the transport cycle which prepares the transporter for substrate translocation by stabilizing an inward-open conformation. We have constructed Markov State Models (MSMs) from extensive molecular dynamics simulations of human DAT (hDAT) to explore the mechanism of this sodium release. Our results quantify the release process triggered by hydration of the Na2 site that occurs concomitantly with a conformational transition from an outward-facing to an inward-facing state of the transporter. The kinetics of the release process are computed from the MSM, and transition path theory is used to identify the most probable sodium release pathways. An intermediate state is discovered on the sodium release pathway, and the results reveal the importance of various modes of interaction of the N-terminus of hDAT in controlling the pathways of release.
多巴胺转运体（DAT）属于神经递质：钠协同转运蛋白（NSS）家族的膜蛋白，负责将神经递质从突触间隙重摄取，以终止神经元信号，并使突触前神经元随后释放神经递质。从晶体学确定的钠离子结合位点 Na2 释放一个钠离子已被确定为转运体对底物易位进行准备的运输循环的初始步骤，通过稳定内向开放构象来实现。我们已经从广泛的人类 DAT（hDAT）分子动力学模拟构建了马尔可夫状态模型（MSM），以探索这种钠离子释放的机制。我们的结果量化了由 Na2 位点的水合触发的释放过程，该过程与转运体从外向到内向构象的构象转变同时发生。从 MSM 计算释放过程的动力学，并使用转移路径理论来确定最可能的钠离子释放途径。在钠离子释放途径上发现了一个中间状态，结果表明 hDAT 的 N 端的各种相互作用模式在控制释放途径中的重要性。
