Expression and functional characterization of an L-rhamnose-binding lectin from Nile tilapia (Oreochromis niloticus) in host defense against bacterial infection

Abstract

Rhamnose-binding lectins (RBLs), a Ca2+-independent lectin family, are able to recognize varieties of pathogens and involve in the innate immune response. In this study, an L-rhamnose-binding lectin-like (OnRBL-1) was identified and functionally characterized from Nile tilapia (Oreochromis niloticus). The open reading frame of OnRBL-1 is 702 bp encoding 233 amino acids. The sequence of OnRBL-1 has relatively conservative characteristic peptide motifs, including YGR, DPC, and KYL-motif. Expression analysis showed that OnRBL-1 was abundantly distributed in liver tissue, and widely existed in all detected tissues. Meanwhile, the expressions of OnRBL-1 increased significantly in vivo (liver, spleen, head kidney, intestine, gills and peripheral blood) and in vitro (hepatocytes) following challenges with two important tilapia pathogenic bacteria Streptococcus agalactiae and Aeromonas hydrophila. Moreover, the recombinant OnRBL-1 was expressed and purified, which was found to bind and agglutinate S. agalactiae and A. hydrophila. Overall, This study indicated that OnRBL-1 may function as an important pattern recognition molecule, possessing recognition and agglutination activity to bacterial pathogens, thus involving in the innate immune defense of O. niloticus.