MG2+ BLOCK AND CA2+ SELECTIVITY IN THE NMDA RECEPTOR

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 谷氨酸受体是脊椎动物中枢神经系统的主要兴奋性受体。NMDA受体是一类由N-甲基-D-天冬氨酸激活的谷氨酸受体，在学习、记忆和许多CNS疾病中起重要作用。NMDA受体离子通道对Na+、K+和Ca 2+是可渗透的。与NMDA受体相关的Ca 2+电流被认为在突触可塑性中是必不可少的，包括诱导长时程增强和长时程抑制。NMDA受体由于Mg 2+阻断而具有强烈的电压依赖性，这是一种具有深刻生理意义的调节机制。在静息电位下，NMDA电流被高度阻断，但膜去极化加剧了Mg 2+阻断。对NMDA受体的结构和功能已经进行了大量的研究，但是NMDA受体的物理结构的关键组分仍然未知。虽然已经有研究记录了特定残基沿着孔和受体跨膜区的其他部分的可及性，但关于总体通道结构和功能的原子水平信息很少，这对于理解Mg 2+阻断和离子选择性很重要。为了研究通道结构，我建立了NMDA受体通道的结构同源性模型，并打算使用结构评分程序来测试其有效性。与NMDA受体一样，NaK通道传导Na+和K+，具有中等程度的序列同源性，并被认为具有与NMDA受体通道相似的结构。同样，KCSA通道和NMDA受体的孔衬里部分被认为是同源的。本实验室的研究生Beth Siegler Retchless建立了一套基于NaK通道的NMDA受体通道的同源模型，成功预测了NR 1上的一个残基和NR 2A上的一个残基相互作用。丹尼尔史密斯也是我实验室的一名研究生，他对这些模型进行了改进。该项目的主要目标是更好地理解NMDA受体通道选择性的物理基础，该通道导致对Ca 2+的高渗透性，但被Mg 2+有效阻断。我们正在使用的技术来研究Ca 2+的选择性正在测试的化学品EGTA（乙二醇四乙酸）和EDTA（乙二胺四乙酸）的分子动力学模型。EGTA和EDTA的结构非常相似。然而，EGTA对Ca 2+的选择性超过Mg 2+，而EDTA不是。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Glutamate receptors are the primary excitatory receptors in the central nervous sytem (CNS) of vertebrates. NMDA receptors, a class of glutamate receptors that are activated by N-methyl-D-aspartate, play an important role in learning, memory, and many CNS disorders. NMDA receptor ion channels are permeable to Na+, K+, and Ca2+. The Ca2+ currents associated with NMDA receptors are believed essential in synaptic plasticity, including induction of long-term potentiation and long-term depression. NMDA receptors feature strong voltage dependence due to Mg2+ block, a regulatory mechanism of profound physiological significance. At resting potentials, NMDA currents are highly blocked, but membrane depolarization alleviates Mg2+ block. There has been much research into the structure and function of NMDA receptors, but key components of the physical structure of NMDA receptors remain unknown. While there have been studies documenting the accessibility of particular residues along the pore and on other portions of the receptor's transmembrane regions, there is little atomic level information on overall channel structure and function, which is important for understanding Mg2+ block and ion selectivity. In order to study channel structure, I have built a structural homology model of the NMDA receptor channel and intend to test its validity using structure scoring programs. The NaK channel, which, like NMDA receptors, conducts Na+ and K+, has a moderate amount of sequence homology and is believed to have similar structure to the NMDA receptor channel. Likewise, the pore lining sections of KCSA channel and NMDA receptors are believed to be homologous. A set of homology models of the NMDA receptor channel based on the NaK channel have built by Beth Siegler Retchless, a graduate student in my lab, which successfully predicted a residue on NR1 and a residue on NR2A that interact with each other. The models have been refined by Daniel Smith, also a graduate student in my lab. The primary goal of this project is to develop a better understanding the physical basis of the selectivity of NMDA receptor channels that results in high permeability to Ca2+ but potent block by Mg2+. The techniques we are using to study Ca2+ selectivity are being tested on molecular dynamics models of the chemicals EGTA (ethylene glycol tetraacetic acid) and EDTA (ethylenediaminetetraacetic acid). The structures of EGTA and EDTA are very similar. However, EGTA is selective for Ca2+ over Mg2+ while EDTA is not.