Novel mannose-specific lectins found in torafugu, Takifugu rubripes: A review

In earlier work, we identified a novel mannose-specific lectin, termed pufflectin-s, from the skin mucus of torafugu, Takifugu rubripes. We here make a brief review on the lectin. The amino acid sequence of pufflectin-s shares sequence homology with mannose-binding lectins of monocotyledonous plants, and has conserved two of three carbohydrate recognition domains, QDNVY motifs, of these plant lectins. By site-directed mutagenesis, we verified that the QDNVY motif in the N-terminal region was critical to the mannose-binding function of pufflectin-s. RT-PCR and Northern blot analyses indicated that the pufflectin-s gene is expressed in the gill, oral cavity wall, esophagus, and skin. In addition, an isoform, pufflectin-i, which shares 91.4% amino acid identity with pufflectin-s, was isolated from the intestine. Using immunohistochemistry, pufflectin-s could be detected exclusively in the epithelial cells of the skin, gill, oral cavity wall and esophagus, whereas pufflectin-i was observed in both mucous and epithelial cells in the intestine. Nevertheless, mRNAs for both pufflectins were detected only in epithelial cells of these tissues with in situ hybridization. Pufflectin-s agglutinated some bacteria isolated from rearing water and from fish skin. This lectin also bound to a parasite, Heterobothrium okamotoi, suggesting that it may play an important role in the self-defense system of fugu.