Transport and Inhibition in a Biogenic Amine Transporter

描述（由申请人提供）：Na？依赖的神经递质转运蛋白或神经递质钠同向转运蛋白（NSS）是完整的膜蛋白，在终止突触传递中起关键作用，因此，在形成突触信号的持续时间和大小方面起关键作用。它们的工作原理是将先前存在的梯度与小分子神经递质从突触到神经元和胶质细胞质的热力学不利运动相结合。生物胺的泵具有特别重要的意义，因为它们的功能障碍与许多使人衰弱的神经精神疾病有关，而且它们是抗抑郁药和可卡因等一系列精神活性药物的目标。尽管具有临床重要性，但底物易位和抑制机制的原子水平细节仍然难以捉摸。原核生物NSS成员LeuT的结构/功能研究已经揭示了这两个主题的关键因素，但由于这种细菌蛋白与真核生物对应蛋白之间的一致性非常低，因此比较必然受到限制。本应用程序的目的是确定LeuT的运输和抑制的分子模型是否也适用于真核NSS成员。这将通过筛选已知的生物胺转运蛋白在异源表达系统的单分散性和他们的结晶倾向来完成。然后将一个代表性的成员结晶，并求解其结构。基于结构的转运和抑制假设随后将通过位点定向诱变、半胱氨酸交联、稳态动力学、解离/关联动力学和晶体学的组合进行测试。虽然确实有很多关于LeuT的研究似乎反映在真核生物的NSS对应物中，但其他领域仍存在不足，因此这些实验的数据将填补一个关键的知识空白。此外，也许更重要的是，真核生物胺转运体的结构研究将允许进一步研究特异性拮抗剂结合位点，甚至可能研究耐药性的分子基础，从而为合理的药物设计工作开辟道路。当最终与超出本应用范围的体内工作相结合时，结构/功能研究也可能揭示致病多态性的分子基础。实现这些目标中的任何一个都可能对实验室和临床产生重大影响。

DESCRIPTION (provided by applicant): Na?dependent neurotransmitter transporters or neurotransmitter sodium symporters (NSS) are integral membrane proteins that play a critical role in terminating synaptic transmission and, thus, in shaping the duration and magnitude of synaptic signaling. They work by coupling preexisting ion gradients to the thermodynamically unfavorable movement of small molecule neurotransmitters from the synapse to neuronal and glial cytoplasms. Pumps for the biogenic amines are of particular significance because their dysfunction has been implicated in a number of debilitating neuropsychiatric diseases and because they are the target of a broad array of psychoactive agents such as antidepressants and cocaine. Despite such clinical importance, atomic-level detail into the mechanism of substrate translocation and inhibition has remained elusive. Structure/function studies of LeuT, a prokaryotic NSS member, has revealed critical elements on both topics, but because the identity between this bacterial protein and the eukaryotic counterparts is so low, the comparisons will necessarily be limited. The goal of this application is to determine if the molecular models of transport and inhibition advanced for LeuT also apply to the eukaryotic NSS members. This will be accomplished by screening known biogenic amine transporters in heterologous expression systems for monodispersity and their propensity for crystallization. A representative member will then be crystallized, and its structure solved. Structure-based hypotheses of transport and inhibition will subsequently be tested with a combination of site-directed mutagenesis, cysteine crosslinking, steady-state kinetics, dissociation/association kinetics, and crystallography. While there is certainly much about LeuT that seems to be reflected in eukaryotic NSS counterparts, other areas fall short, so data from these experiments will fill a critical intellectual void. In addition, and perhaps more importantly, structural studies of a eukaryotic biogenic amine transporter will permit further investigation into specific antagonist binding sites and perhaps into the molecular basis for drug resistance, thereby opening the way to rational drug design efforts. When eventually coupled with in vivo work beyond the scope of this application, structure/function studies may also shed light on the molecular underpinnings of disease-causing polymorphisms. Achieving any one of these objectives would likely have significant impact in both the laboratory and in the clinic.