Structural basis of ligand binding in plant glutamate receptor homologues

在动物的神经系统中，嗜离子性谷氨酸受体介导神经细胞之间的化学通讯。植物没有神经系统，但拥有谷氨酸受体同源蛋白，参与根系发育、离子运输、信号传导和代谢。直到最近，还没有人能够对这些植物谷氨酸受体同源物进行功能表征。我现在展示了拟南芥20个亚基中的一个，AtGLR1.4，它形成了一个配体门控制的阳离子通道就像动物谷氨酸受体亚基一样。然而，这种受体不感知谷氨酸，而是感知许多不同的氨基酸，一些作为激动剂，一些作为拮抗剂，具有不同的效果。该项目的目的是阐明这种新颖的、异常广泛的AtGLR1.4配体选择性的结构基础。为此，将大规模构建、表达和纯化可溶形式的At-GLR1.4配体结合域。然后将可溶性配体结合域与不同的氨基酸配体进行表征和结晶，以获得x射线结构。这些结构将提供对广泛配体选择性的相互作用以及受体激活机制的深入了解。

In the nervous systems of animals, ionotropic glutamate receptors mediate chemical communication between nerve cells. Plants lack a nervous system, but possess proteins homologous to glutamate receptors, which have been implicated in root development, ion transport, signalling, and metabolism. Until recently, nobody had been able to functionally characterise any of these plant glutamate receptor homologues. I now showed for one of the twenty subunits from Arabidopsis thaliana – AtGLR1.4 – that it forms a ligand-gated cation channel just like the animal glutamate receptor subunits. However, this receptor does not sense glutamate but a number of different amino acids, some acting as agonists, some as antagonists with varying efficacies. The aim of the proposed project is to elucidate the structural basis of this novel, unusually broad ligand selectivity of AtGLR1.4. To this end, a soluble form of the At-GLR1.4 ligand binding domain will be constructed, expressed, and purified on a large scale. The soluble ligand binding domain will then be characterised and crystallised in complex with different amino acid ligands to obtain X-ray structures. These structures will provide insight into the interactions responsible for the broad ligand selectivity as well as into the mechanism of receptor activation.