Functional Validation of Heteromeric Kainate Receptor Models

Abstract

It is been shown that homomeric kainate receptors require external ions for gating. However, in vivo, kainate receptors are most likely arranged as heterotetramers and the extent to which external ions are required for gating is less clear. A large amount of structural and biochemical work over the years has indicated that agonists bind to the ligand-binding domain (LBD), which is arranged as a dimer of dimers as exemplified in homomeric structures. However, no high-resolution structure currently exists of heteromeric kainate receptors and in a full-length heterotetramer, the LBDs could potentially be arranged either as a GluK2 homomer alongside a GluK5 homomer or as two GluK2/K5 heterodimers. To investigate this further we built models of the LBD dimers based on the GluK2 LBD crystal structures and investigated their stability with molecular dynamics simulations. The models were then used to make predictions about the functional behavior of the full-length GluK2/K5 receptor including the anticipation that lithium ions would bind to the dimer interface of GluK2/K5 heteromers and slow their desensitization. These predictions were confirmed via electro- physiological recordings giving high confidence in the models suggesting they find future use in the absence of high-resolution crystallographic or NMR data.