An adherens junction protein is a member of the family of lactose-binding lectins.

We previously described a pig junction protein of M(r) 37,000 found in oral epithelium but not in epidermis, limited to suprabasal cells, and colocalizing by immunofluorescence with adherens junction proteins. A 1.1-kilobase pair cDNA of the 37-kDa protein yielded an open reading frame encoding a 323-amino acid protein of 35,852 Da, and Northern analysis demonstrated a band of 1.2 kilobases in tongue RNA. Secondary structure predictions indicate that the 37% identical 16-17-kDa N- and C-terminal domains from beta-sheet-rich barrels linked by a compact proline-rich segment. The protein is 72% identical in amino acid sequence and shares symmetrical two-domain structure with L-36, a lectin of unknown function from rat intestine, indicating that the 37-kDa protein is the porcine form of L-36. Of the homologous lactose binding lectins known, two others, invertebrate lectins, share this symmetrical structure. Expression of the C-terminal domain of the pig lectin in bacteria yields a lectin which binds lactosyl-Sepharose, and binding is inhibited by lactose. The expressed protein binds a glycoprotein of 120 kDa from pig tongue epithelium on Western blots, and this is also inhibited by lactose. The findings suggest that the lectin function may be involved in the assembly of adherens junctions.