Correlating efficacy and desensitization with GluK2 ligand-binding domain movements
Correlating efficacy and desensitization with GluK2 ligand-binding domain movements
复制标题
将功效和脱敏与 GluK2 配体结合域运动相关联
作者：
N. Nayeem;O. Mayans;T. Green
AMPA和红藻氨酸盐选择性离子型谷氨酸受体的门控可以根据配体亲和力、效力以及脱敏的速率和程度来定义。对所有三个元素的关键见解来自配体结合结构域（LBD）的结构研究。特别是，结合裂隙闭合与疗效相关，而由相邻LBD形成的二聚体的解离与脱敏相关。我们已经探索了这些关系中的红藻氨酸选择性亚基GluK 2通过研究突变的两个残基（K531和R775），形成关键接触内的LBD二聚体界面，但其截断意外衰减脱敏的影响。一个突变（K531 A）也改变了谷氨酸和红藻氨酸的相对功效。结合这些突变的LBD晶体结构揭示了几种构象变化，共同解释了它们的表型。K531截短导致新的二聚体接触，这与与效力相关的配体结合裂缝中的较慢脱敏和侧向移动一致。测试的突变体还破坏阴离子结合;在二聚体界面位点中未检测到氯离子，包括在R775 A中，其中氯离子的缺失是唯一明显的结构变化。由此，我们提出，在GluK 2 LBD二聚体界面的电荷平衡保持一定程度的不稳定性，快速和完全脱敏所必需的。
Gating of AMPA- and kainate-selective ionotropic glutamate receptors can be defined in terms of ligand affinity, efficacy and the rate and extent of desensitization. Crucial insights into all three elements have come from structural studies of the ligand-binding domain (LBD). In particular, binding-cleft closure is associated with efficacy, whereas dissociation of the dimer formed by neighbouring LBDs is linked with desensitization. We have explored these relationships in the kainate-selective subunit GluK2 by studying the effects of mutating two residues (K531 and R775) that form key contacts within the LBD dimer interface, but whose truncation unexpectedly attenuates desensitization. One mutation (K531A) also switches the relative efficacies of glutamate and kainate. LBD crystal structures incorporating these mutations revealed several conformational changes that together explain their phenotypes. K531 truncation results in new dimer contacts, consistent with slower desensitization and sideways movement in the ligand-binding cleft correlating with efficacy. The tested mutants also disrupted anion binding; no chloride was detected in the dimer-interface site, including in R775A where absence of chloride was the only structural change evident. From this, we propose that the charge balance in the GluK2 LBD dimer interface maintains a degree of instability, necessary for rapid and complete desensitization.