Agonist binding to the GluK5 subunit is sufficient for functional surface expression of heteromeric GluK2/GluK5 kainate receptors
Agonist binding to the GluK5 subunit is sufficient for functional surface expression of heteromeric GluK2/GluK5 kainate receptors
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DOI：
10.1007/s10571-013-9976-x
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发表时间：
2013-11-01
影响因子：
4
通讯作者：
Housley, Paul R.
中科院分区：
文献类型：
--
作者：
Fisher, Janet L.;Housley, Paul R.
向质膜运输嗜离子性谷氨酸受体通常需要占据激动剂结合位点。这种质量控制检查通常不涉及受体激活，因为竞争性拮抗剂或非功能性通道的结合也可能允许表面表达。四聚体盐酸盐受体可以由五种不同的亚基（GluK1-GluK5）组装而成。“低亲和力”的GluK1-3亚基能够产生功能性同质受体，而“高亲和力”的GluK4和GluK5亚基需要与GluK1、2或3共组装才能在表面表达。这两种不同类型的亚基在受体中具有不同的功能作用。因此，我们研究了占据GluK2或GluK5亚基激动剂位点对异质受体表面表达的相对重要性。我们在S2配体结合域内创建了一个突变亚基，降低了激动剂的亲和力。该位点的突变降低了同源GluK2受体的功能性表面表达，但这些受体的表面表达可以通过竞争拮抗剂或与野生型GluK5共组装而增加。相反，GluK5亚基的突变减少了膜上功能性异聚体受体的产生，并且不能用拮抗剂或野生型GluK2来挽救。这些发现表明，配体仅与GluK5亚基结合是允许重组GluK2/K5异聚体运输到细胞膜的必要和充分条件，但仅占有GluK2位点不是必要条件。我们的研究结果表明，GluK5亚基在调节异聚盐酸盐受体的表面表达中起着独特的作用。
Trafficking of ionotropic glutamate receptors to the plasma membrane commonly requires occupation of the agonist binding sites. This quality control check does not typically involve receptor activation, as binding by competitive antagonists or to non-functional channels may also permit surface expression. The tetrameric kainate receptors can be assembled from five different subunits (GluK1-GluK5). While the "low-affinity" GluK1-3 subunits are able to produce functional homomeric receptors, the "high-affinity" GluK4 and GluK5 subunits require co-assembly with GluK1, 2, or 3 for surface expression. These two different types of subunits have distinct functional roles in the receptor. Therefore, we examined the relative importance of occupancy of the agonist site of the GluK2 or GluK5 subunit for surface expression of heteromeric receptors. We created subunits with a mutation within the S2 ligand-binding domain which decreased agonist affinity. Mutations at this site reduced functional surface expression of homomeric GluK2 receptors, but surface expression of these receptors could be increased with either a competitive antagonist or co-assembly with wild-type GluK5. In contrast, mutations in the GluK5 subunit reduced the production of functional heteromeric receptors at the membrane, and could not be rescued with either an antagonist or wild-type GluK2. These findings indicate that ligand binding to only the GluK5 subunit is both necessary and sufficient to allow trafficking of recombinant GluK2/K5 heteromers to the cell membrane, but that occupancy of the GluK2 site alone is not. Our results suggest a distinct role for the GluK5 subunit in regulating surface expression of heteromeric kainate receptors.