Coassembly of two GluR6 Kainate receptor splice variants within a functional protein complex

Kainate receptors (KAR) are composed of several distinct subunits and splice variants, but the functional relevance of this diversity remains largely unclear. Here we show that two splice variants of the GluR6 subunit, GIuR6a and GIuR6b, which differ in their C-terminal domains, do not show distinct functional properties, but coassemble as heteromers in vitro and in vivo. Using a proteomic approach combining affinity purification and MALDI-TOF mass spectrometry, we found that GluR6a and GIuR6b interact with two distinct subsets of cytosolic proteins mainly involved in W regulation of channel function and intracellular trafficking. Guided by these results, we provide evidence that the regulation of native KAR function by NMDA receptors depends on the heteromerization of GIuR6a and GIuR6b and interaction of calcineurin with GIuR6b. Thus, GIuR6a and GIuR6b bring in close proximity two separate subsets of interacting proteins that contribute to the fine regulation of KAR trafficking and function.