A novel sialic acid binding lectin with anti-bacterial activity from the Hong Kong oyster (Crassostrea hongkongensis).

Lectins play an important role in immune recognition and host defense. In the present study, a full-length cDNA encoding a novel sialic acid binding lectin was cloned from Crassostrea hongkongensis (designated Ch-salectin) by rapid amplification of cDNA ends (RACE). It is 531 bp in length, containing a 21 bp 5' UTR, a 39 bp 3' UTR and a 468 bp ORF coding for 156 amino acids. The Ch-salectin protein contains a signal peptide and a conserved complement component C1q domain. The purified recombinant MBP-tagged Ch-salectin protein can bind to a sialic acid containing protein fetuin and significantly inhibit the growth of both Gram-negative and Gram-positive bacteria. Furthermore, the transcription of Ch-salectin was inducible and significantly up-regulated during Vibrio alginolyticus infection. Thus, these results highlight the essential roles of Ch-salectin in immune recognition and host defense against bacterial infection in C. hongkongensis.