Postsynaptic density scaffolding protein. Binds and cross-links cytoplasmic regions of GRM1， GRM5， ITPR1， DNM3， RYR1， RYR2， SHANK1 and SHANK3. By physically linking GRM1 and GRM5 with ER-associated ITPR1 receptors， it aids the coupling of surface receptors to intracellular calcium release. Isoforms can be differently regulated and may play an important role in maintaining the plasticity at glutamatergic synapses. Negatively regulates T cell activation by inhibiting the calcineurin-NFAT pathway. Acts by competing with calcineurin/PPP3CA for NFAT protein binding， hence preventing NFAT activation by PPP3CA (PubMed:18218901).