Required for synapse integrity and synaptic plasticity. During cerebellar synapse formation, essential for the formation and maintenance of parallel fiber and Purkinje cell synapses. When parallel fibers make contact with Purkinje spines, CBLN1 interaction with GRID2 triggers the recruitment of NRXN1 and secretory vesicles to the sites of contact. NRXN1-CBLN1-GRID2 signaling induces presynaptic morphological changes, which may further accumulate pre- and postsynaptic components to promote bidirectional maturation of parallel fiber - Purkinje cell functionnally active synapses by a positive feedback mechanism. Required for CBLN3 export from the endoplasmic reticulum and secretion (By similarity).