The Neurotransmitter: Sodium Symporter Permeation Pathway

描述（由申请人提供）：生物胺转运蛋白在其特定神经递质底物的作用和再循环中发挥重要作用。它们已被确定为许多影响脑功能的药物的靶点。例如，可卡因的奖励性质主要是由于其抑制多巴胺转运蛋白（DAT）;丙咪嗪的抗抑郁作用是对5-羟色胺转运蛋白（SERT）产生的。这些转运蛋白属于神经递质钠同向转运蛋白（NSS）家族，该家族具有大量原核同源物，包括色氨酸转运蛋白（TnaT）、酪氨酸转运蛋白（Tyt 1）和亮氨酸转运蛋白（LeuT）。最近，LeuT结构已经在高分辨率下得到解决，其中衬底Leu被束缚在封闭的腔中。然而，底物特异性的决定因素，理解这一点对于合理的药物设计是重要的，可能不仅存在于LeuT结构所揭示的结合位点裂缝内，而且还存在于沿着渗透途径。本提案的长期目标是阐明NSS家族蛋白在易位周期中渗透途径的动态结构变化，并评估竞争性转运模型，例如。例如，在一个实施例中，交替访问方案和衬底跳跃模型。具体而言，使用原核NSS蛋白，TnaT，Tyt 1和LeuT作为模型系统，这将通过分子建模模拟和实验研究/验证之间的集成，比较迭代过程来实现。这个多学科的协议，我们将探讨保守的残基位置和潜在的辅助腔线的渗透途径，并在不同的构象状态动态重组。的共同点，和不同的功能的渗透途径，包括钠离子的作用，将比较之间的TnaT/Tyt 1/LeuT，并与其他原核和真核NSS-蛋白。所获得的知识应该阐明生物胺转运蛋白的易位周期，并将有助于我们理解底物特异性的结构基础。

DESCRIPTION (provided by applicant): Biogenic amine transporters play important roles in the action and recycling of their specific neuretransmitter substrates. They have been well established as the targets for many pharmacological agents that affect brain function. For examples, the rewarding properties of cocaine are due mainly to its inhibition of dopamine transporter (DAT); the antidepressant effect of imipramine is exerted on serotonin transporter (SERT). These transporters belong to the NeurotransmitterSodium Symporter (NSS) family, which has a large number of prokaryotic homologs, including a tryptophan transporter (TnaT), a tyrosine transporter (Tyt1), and a leucine transporter (LeuT). Recently, a LeuT structure has been solved in high resolution, with the substrate Leu bound in an enclosed cavity. However, the determinants of substrate specificity, an understanding of which is important for rational drug design, may lie not only within the binding site crevice revealed by the LeuT structure, but also along the permeation pathway. The long term goal of the present proposal is to elucidate dynamic structural changes of the permeation pathway of NSS family proteins during the translocation cycle and to evaluate competing transport models, e. g., the alternating-access scheme and the substrate hopping model. Specifically, using prokaryotic NSS-proteins, TnaT, Tyt1, and LeuT as model systems, this will be achieved by an integrated, comparative process of iteration between molecular modeling simulations and experimental investigations/validations. With this multidisciplinary protocol we will explore the conserved residue positions and potential auxiliary cavities that line the permeation pathway and reorganize dynamically in different conformational states. The common, and the different features of the permeation pathways, including the roles of sodium ions, will be compared among TnaT/Tyt1/LeuT, and with other prokaryotic and eukaryotic NSS-proteins. The knowledge acquired should shed light on the translocation cycles of biogenic amine transporters and will contribute to our understanding of the structural bases of substrate specificities.