Enables glutamate receptor binding activity and protein homodimerization activity. Involved in intracellular protein transport and positive regulation of synapse assembly. Located in early endosome membrane; postsynaptic density membrane; and synaptic vesicle membrane. Is integral component of plasma membrane. Orthologous to human SYNDIG1 (synapse differentiation inducing 1). [provided by Alliance of Genome Resources, Apr 2022]