Transport and Inhibition in a Biogenic Amine Transporter

描述（由申请人提供）：Na？依赖性神经递质转运体或神经递质钠共转运体（NSS）是在终止突触传递中起关键作用的整合膜蛋白，因此在形成突触信号传导的持续时间和幅度中起关键作用。它们通过将预先存在的离子梯度耦合到小分子神经递质从突触到神经元和神经胶质细胞的有害运动来工作。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，并且因为它们是广泛的精神活性剂如抗抑郁药和可卡因的靶点。尽管有这样的临床重要性，原子级的底物易位和抑制机制的细节仍然难以捉摸。LeuT，原核NSS成员的结构/功能研究，揭示了这两个主题的关键要素，但由于这种细菌蛋白质和真核生物的对应物之间的身份是如此之低，比较必然是有限的。本申请的目的是确定LeuT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蛋白的单分散性及其结晶倾向来实现。一个代表性的成员将被结晶化，其结构将被解析。随后将结合定点诱变、半胱氨酸交联、稳态动力学、解离/缔合动力学和晶体学对基于结构的转运和抑制假设进行测试。虽然LeuT在真核NSS对应物中有很多反映，但其他领域还不够，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，真核生物胺转运蛋白的结构研究将允许进一步调查到特定的拮抗剂结合位点，并可能进入耐药性的分子基础，从而开辟了合理的药物设计的努力。当最终与超出本申请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.