Acts as a synaptic organizer in specific subsets of neurons in the brain (By similarity). Essential for the formation and maintenance of inhibitory GABAergic synapses (By similarity). Promotes the development of dendrite-targeting inhibitory GABAergic synapses made by somatostatin-positive interneurons (By similarity). May contribute to the function of ventral medial habenula region of the brain implicated in the regulation of anxiety-related behaviors (By similarity). May play a role in CBLN3 export from the endoplasmic reticulum and secretion (By similarity). Homohexamer; disulfide-linked homotrimers. The trimers are assembled via the globular C1q domains. The trimers associate via N-terminal cysteine residues to form disulfide-linked hexamers (By similarity). May form oligomers with CBLN1, CBLN2 and CBLN3 prior to secretion (By similarity). Strongly interacts with DCC in a NTN1-displaceable fashion (By similarity). Weakly binds to NRXN1 and NRXN2 long and short isoforms produced by alternative promoter usage. Interaction with NRXN3 short isoform is hardly detectable; no interaction at all with NRXN3 long isoform (By similarity). Detected at GABAergic synapses. Sialoglycoprotein.