May be involved in synaptic functions in the CNS. Heterohexamer; disulfide-linked heterotrimers. Interacts with CBLN1. May also form oligomers with CBLN2 AND CBLN4 (By similarity). 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 (By similarity).