May be involved in synaptic functions in the CNS. Heterohexamer; disulfide-linked heterotrimers (By similarity). Interacts with CBLN1. May also form oligomers with CBLN2 AND CBLN4. In the absence of CBLN1, remains in the endoplasmic reticulum/cis-Golgi apparatus. Partial secretion depends on an association with CBLN1 and maybe CBLN4, but not on CBLN2. Expressed in brain, restricted to the cerebellar cortex. Within the cerebellum, expressed in granule layers (at protein level). Also detected in postsynaptic Purkinje cell spines (at protein level). In the developing brain, selectively expressed as early as postnatal day 7-10 in cerebellar granule cells.