Identification and Characterization of a Novel Lectin from the Clam Glycymeris yessoensis and Its Functional Characterization under Microbial Stimulation and Environmental Stress

Lectin from the bivalve Glycymeris yessoensis (GYL) was purified by affinity chromatography on porcine stomach mucin-Sepharose. GYL is a dimeric protein with a molecular mass of 36 kDa, as established by SDS-PAGE and MALDI-TOF analysis, consisting of 18 kDa subunits linked by a disulfide bridge. According to circular dichroism data, GYL is a beta/alpha-protein with the predominance of beta-structure. GYL preferentially agglutinates enzyme-treated rabbit erythrocytes and recognizes glycoproteins containing O-glycosidically linked glycans, such as porcine stomach mucin (PSM), fetuin, thyroglobulin, and ovalbumin. The amino acid sequences of five segments of GYL were acquired via mass spectrometry. The sequences have no homology with other known lectins. GYL is Ca2+-dependent and stable over a range above a pH of 8 and temperatures up to 20 degrees C for 30 min. GYL is a pattern recognition receptor, as it binds common pathogen-associated molecular patterns, such as peptidoglycan, LPS, beta-1,3-glucan and mannan. GYL possesses a broad microbial-binding spectrum, including Gram-positive (Bacillus subtilis, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Vibrio proteolyticus), but not the fungus Candida albicans. Expression levels of GYL in the hemolymph were significantly upregulated after bacterial challenge by V. proteolyticus plus environmental stress (diesel fuel). Results indicate that GYL is probably a new member of the C-type lectin family, and may be involved in the immune response of G. yessoensis to bacterial attack.