Promotes neurite outgrowth in hippocampal neurons. Involved in the regulation and maintenance of excitatory synapses. Induces the clustering of excitatory postsynaptic proteins, including DLG4, DLGAP1, GRIA1 and GRIN1. Can form heteromeric complexes with LRFN2, LRFN3, LRFN4 and LRFN5. Forms homomeric complexes, but not across cell junctions. Interacts with DLG4. Interacts also with DLG1, DLG2, and DLG3 (By similarity). Interacts with 2 AMPA receptor subunits GRIA1 and GRIA2 and NMDA receptor subunit GRIN1. Detected in excitatory, but not inhibitory, synaptic plasma membrane. Predominantly expressed in the brain, with a weak, but broad expression in the cerebral cortex and diencephalic nuclei. Also detected in other parts of the central nervous system, including the olfactory bulb, pons, cerebellum, and medulla oblongata, as well as in the peripheral nervous system, such as the ganglia of cranial nerves and the dorsal root ganglion during gestation. Expression starts around 10.5 dpc. At 11.5 dpc, broadly expressed in the telencephalic and diencephalic vesicles. This pattern of expression continues until 17.5 dpc. The PDZ-binding motif is required for neurite outgrowth promotion. This motif is also involved in DLG1-, DLG3- and DLG4-binding (By similarity). Glycosylated. Belongs to the LRFN family.