Mayer Mark L, Ghosal Alokesh, Dolman Nigel P, Jane David E
Porter Neuroscience Research Center, National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892, USA.
J Neurosci. 2006 Mar 15;26(11):2852-61. doi: 10.1523/JNEUROSCI.0123-06.2005.
Glutamate receptor (GluR) ion channels mediate fast synaptic transmission in the mammalian CNS. Numerous crystallographic studies, the majority on the GluR2-subtype AMPA receptor, have revealed the structural basis for binding of subtype-specific agonists. In contrast, because there are far fewer antagonist-bound structures, the mechanisms for antagonist binding are much less well understood, particularly for kainate receptors that exist as multiple subtypes with a distinct biology encoded by the GluR5-7, KA1, and KA2 genes. We describe here high-resolution crystal structures for the GluR5 ligand-binding core complex with UBP302 and UBP310, novel GluR5-selective antagonists. The crystal structures reveal the structural basis for the high selectivity for GluR5 observed in radiolabel displacement assays for the isolated ligand binding cores of the GluR2, GluR5, and GluR6 subunits and during inhibition of glutamate-activated currents in studies on full-length ion channels. The antagonists bind via a novel mechanism and do not form direct contacts with the E723 side chain as occurs in all previously solved AMPA and kainate receptor agonist and antagonist complexes. This results from a hyperextension of the ligand binding core compared with previously solved structures. As a result, in dimer assemblies, there is a 22 A extension of the ion channel linkers in the transition from antagonist- to glutamate-bound forms. This large conformational change is substantially different from that described for AMPA receptors, was not possible to predict from previous work, and suggests that glutamate receptors are capable of much larger movements than previously thought.
谷氨酸受体（GluR）离子通道介导哺乳动物中枢神经系统中的快速突触传递。众多晶体学研究，其中大部分是关于GluR2亚型的AMPA受体，揭示了亚型特异性激动剂结合的结构基础。相比之下，由于拮抗剂结合结构要少得多，因此对拮抗剂结合机制的了解要少得多，特别是对于作为由GluR5 - 7、KA1和KA2基因编码的具有独特生物学特性的多种亚型存在的海人酸受体。我们在此描述了GluR5配体结合核心复合物与新型GluR5选择性拮抗剂UBP302和UBP310的高分辨率晶体结构。晶体结构揭示了在对GluR2、GluR5和GluR6亚基的分离配体结合核心进行放射性标记置换测定以及在全长离子通道研究中抑制谷氨酸激活电流期间观察到的对GluR5的高选择性的结构基础。拮抗剂通过一种新机制结合，并且不像所有先前解析的AMPA和海人酸受体激动剂及拮抗剂复合物那样与E723侧链形成直接接触。这是由于与先前解析的结构相比，配体结合核心过度伸展所致。结果，在二聚体组装中，从拮抗剂结合形式转变为谷氨酸结合形式时，离子通道连接体延长了22埃。这种大的构象变化与AMPA受体所描述的有很大不同，无法从先前的工作中预测，这表明谷氨酸受体能够进行比先前认为的更大的运动。
