Transport and Inhibition in a Biogenic Amine Transporter

描述(由申请人提供)：钠依赖神经递质转运体或神经递质钠转运体(NSS)是一种完整的膜蛋白，在终止突触传递，从而决定突触信号的持续时间和大小方面发挥关键作用。它们的工作原理是将预先存在的离子梯度与小分子神经递质从突触到神经元和神经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靶标。尽管有如此重要的临床意义，关于底物转位和抑制机制的原子水平的细节仍然是难以捉摸的。Leut是原核生物NSS成员，其结构/功能研究揭示了这两个主题的关键元件，但由于这种细菌蛋白与真核对应蛋白之间的同源性很低，因此比较必然是有限的。这项应用的目的是确定为Leut提出的转运和抑制的分子模型是否也适用于真核NSS成员。这将通过在异源表达系统中筛选已知的生物胺转运体来实现，以确定其单分散性和结晶倾向。然后，一个具有代表性的成员将被结晶，其结构将被解决。随后将结合定点突变、半胱氨酸交联、稳态动力学、解离/缔合动力学和结晶学来检验基于结构的转运和抑制假说。虽然确实有很多关于Leut的信息似乎反映在了真核NSS的对应物中，但其他领域却存在不足，因此这些实验的数据将填补一个关键的学术空白。此外，也许更重要的是，对真核生物原胺转运体的结构研究将有助于进一步研究特定的拮抗剂结合部位，并可能进一步研究耐药的分子基础，从而为合理的药物设计努力开辟道路。当最终与超出这一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基因多态的分子基础。实现这些目标中的任何一个都可能在实验室和临床上产生重大影响。

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.