Identification of the Ca²⁺/calmodulin-dependent protein kinase II regulatory phosphorylation site in the α-amino-3-hydroxyl-5-methyl-4- isoxazole-propionate-type glutamate receptor

Ca²⁺/CaM-dependent protein kinase II (CaM-KII) can phosphorylate and potentiate responses of α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate- type glutamate receptors in a number of systems, and recent studies implicate this mechanism in long term potentiation, a cellular model of learning and memory. In this study we have identified this CaM-KII regulatory site using deletion and site-specific mutants of glutamate receptor 1 (GIuR1). Only mutations affecting Set⁸³¹ altered the ³²P peptide maps of GluR1 from HEK-293 cells co- expressing an activated CaM-KII. Likewise, when CaM-KII was infused into cells expressing GluR1, the Ser⁸³¹ to Ala mutant failed to show potentiation of the GluR1 current. The Ser⁸³¹ site is specific to GluR1, and CaM-KII did not phosphorylate or potentiate current in cells expressing GluR2, emphasizing the importance of the GluR1 subunit in this regulatory mechanism. Because Set⁸³¹ has previously been identified as a protein kinase C phosphorylation site (Roche. K. W., O'Brien, R. J., Mammen, A. L., Bernhardt, J., and Huganir, R. L. (1996) Neuron 16, 1179-1188), this raises the possibility of synergistic interactions between CaM-KII and protein kinase C in regulating synaptic plasticity.