Structural basis of ligand binding in plant glutamate receptor homologues

在动物的神经系统中，离子型谷氨酸受体介导神经细胞之间的化学通讯。植物缺乏神经系统，但拥有与谷氨酸受体同源的蛋白质，谷氨酸受体与根发育、离子运输、信号传递和新陈代谢有关。直到最近，还没有人能够从功能上描述这些植物谷氨酸受体的同源物。我现在展示了来自拟南芥的20个亚基中的一个-AtGLR1.4-它形成了一个配体门控的阳离子通道，就像动物的谷氨酸受体亚基一样。然而，这种受体并不感知谷氨酸，而是一些不同的氨基酸，一些作为激动剂，一些作为拮抗剂，但效果各不相同。拟议项目的目的是阐明AtGLR1.4这种新颖的、异常广泛的配体选择性的结构基础。为此，将构建、表达和大规模纯化AT-GLR1.4配体结合域的可溶性形式。然后，可溶的配体结合区域将被表征，并在与不同氨基酸配体的络合物中结晶，以获得X射线结构。这些结构将有助于深入了解导致广泛配体选择性的相互作用以及受体激活的机制。

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.