OPCML comprises 7 exons, spans approximately 600 kb and is transcribed from telomere to centromere. Sequence analysis of the OPCML promoter revealed a GC-rich region spanning 900 bp approximate 500 bp upstream of the translational start site.

OPCML consisted of one half beta-sheets and one fourth alpha-helices. Hydropathy analysis suggested that hydrophobic and hydrophilic regions were evenly distributed along the sequence, but the NH2- and COOH-termini were hydrophobic. Hydrophobic moments and Fourier-transform amphipathic analyses further suggest that residues 23-30 and 83-93 were amphipathic beta-sheets. Structural elements include three, with the first and third being full C2 domains and the middle domain being a truncated C2 domain, and a GPI anchor. Protein is extensively glycosylated with six potential N-linked sites.

OPCML is highly expressed in the nervous system and involved in cell adhesion and cell-cell recognition. During the first postnatal week, protein is prominent within cerebral cortex, developing hippocampus, pyriform cortex, and the mitral cell layer of the olfactory bulb. At later ages, OPCML is expressed prominently within all regions of Ammons horn and in the mitral cell layer of the olfactory bulb and the pyriform cortex. OPCML is localized preferentially to dendrites compared with somata and terminals of hypothalamic vasopressin-secreting magnocellular neurons. This localization indicates that protein is one of the dendrite-associated cell adhesion molecules. It is synthesized within the somata, attached to vasopressin neurosecretory granules via the glycosylphosphatidylinositol anchor, and transported to the dendrites. Moreover, the subcellular localization of OPCML is changed in an activity-dependent manner.
Recently published data suggested that OPCML-v1 was widely expressed in all normal adult and fetal tissues except for placenta and peripheral blood mononuclear cells, though at varying levels (highly expressed in brain, kidney, spleen, stomach, trachea, testis, cervix, ovary and prostate, and weakly in lung, breast, and bone marrow). Compared to v1, OPCML-v2 displayed a more tissue-specific expression pattern in adult tissues, with expression absent or barely detectable in kidney, spleen, pancreas, breast, testis, lung, colon, liver, testis and bone marrow. In contrast to its expression in adult tissues, OPCML-v2 was expressed at moderate to high levels in all fetal tissues except for placenta.

OPCML was originally isolated as a potential micro-type opiate receptor. Subsequent studies have shown that the physiologic opiate receptors belong to the G-protein-coupled receptor family, however, they do not promote direct binding of opioids when transfected into heterologous cells. IgLONs have been suggested to play an important role in cell adhesion and cell-cell recognition, through both homo- and heterophilic interactions within the family. Recently, it has been proposed that IgLONs function mainly as heterodimers called Diglons. OPCML may contribute to the diversity at the surface of different populations of neurons during development. Some latest evidences also suggest that OPCML is a synaptic cell adhesion molecule concerning synaptogenesis and its surface localization is dynamically regulated in response to neuronal activity. Recently, it has been shown that IgLONs are expressed outside the nervous system, and OPCML might act as a tumor suppressor. As a cell adhesion molecule, OPCML comprises several protein-protein interaction domains, commonly found in cell surface- adhesion and receptor molecules. Through these domains, OPCML may bind directly to growth promoting or inhibitory molecules and modulate their functions in tumor cells.
New findings suggested that OPCML is an excellent candidate for tumor suppressor gene (TSG). OPCML is frequently somatically inactivated in cancer by allele loss and by CpG island methylation. OPCML has functional characteristics consistent with TSG properties both in vitro and in vivo. It has been found existence somatic missense mutation in individual with epithelial ovarian cancer and it shows clear evidence of loss of function. Another data showed that OPCML gene promoter methylation may play an important role in the carcinogenesis of cervical and lung carcinoma. OPCML probably functions as a tumor suppressor through interacting with other IgLONs to form heterodimeric complex involved in signal transduction. Among the IgLON family, OPCML was the first member reported to possess tumor suppressor functions in epithelial ovarian cancer, being frequently silenced genetically and epigenetically at the early step of ovarian carcinogenesis. This inactivation is due to its promoter methylation, which further impairs its response to environmental stresses. Loss of OPCML reduces the intercellular adhesion and heterodimeric complex formation and thus impairs the corresponding signaling pathways, thereby promoting the progress of carcinogenesis. Latest evidences of Cui et al (2008) suggested that OPCML is frequently inactivated epigenetically in multiple tumor cell line including nasopharyngeal, esophageal, lung, gastric, hepatocellular, colorectal, breast, cervical and prostate carcinomas. Authors showed that OPCML is a stress-responsive and p53-regulated gene, with the response abrogated when the promoter becomes methylated. Ectopic expression of OPCML in tumor cell lines with endogenous silencing led to strong inhibition of cell colony formation, dramatic anchorage-dependent and - independent growth inhibition demonstrating that OPCML acts as a broad tumor suppressor. The role of OPCML in DNA damage repair, apoptosis and cell cycle arrest with respect to stress response remains to be further investigated.

Two alternative splice transcripts of OPCML, variant 1 (v1) and variant 2 (v2), were previously identified in human, which differ only in their 59 exons but encode an identical mature protein. Among the four IgLON family members, OPCML shares the highest homology to HNT that lies approximately 80 kb centromeric to OPCML in the opposite orientation. Notably, the coding region in exon 1 of OPCML-v1 and HNT is identical, and so is the exon 2 except for only several bases. The first Ig domains of these two proteins share 92% identity, while the second and third Ig domains share 70% and 66% identity, respectively. This raises the possibility that OPCML and HNT may originate from the same antecestor by gene conversion during evolution.