Mouse Homer Protein Homolog 1, HOMER1 ELI

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.

May also couple GRM1 to PI3 kinase through its interaction with AGAP2.

Isoform 1 regulates the trafficking and surface expression of GRM5.

Differentially regulates the functions of the calcium activated Channel ryanodine receptors RYR1 and RYR2.

Isoform 1 decreases the activity of RYR2, and increases the activity of RYR1, whereas isoform 5 counteracts the effects by competing for binding sites.

Isoform 3 regulates the trafficking and surface expression of GRM5.

Isoform 5 acts as a natural dominant negative, in dynamic competition with constitutively expressed isoform 1, isoform 2 and isoform 3 to regulate synaptic metabotropic glutamate function.

Isoform 5, may be involved in the structural changes that occur at synapses during long-lasting neuronal plasticity and development (By similarity).

Forms a high-order complex with SHANK1, which in turn is necessary for the structural and functional integrity of dendritic spines (By similarity).

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 (By similarity).