Molecular characterization and biological function of a tandem-repeat galectin-9 in Qihe crucian carp Carassius auratus.

Galectin-9, as one of the important PRRs in host, could initiate the immune defense responses through recognizing and binding PAMPs on the surface of invading microorganisms. In this study, a new galectin-9 cDNA was identified and characterized in Qihe crucian carp Carassius auratus (named as CaGal-9). The complete cDNA sequence of CaGal-9 was 1318 bp, with an open reading frame (ORF) of 963 bp encoding 320 amino acids. The predicted CaGal-9 protein contained two non-identical carbohydrate recognition domains (CRDs), which possessed the representative motifs H-NPR and WG-EER to bind with β-galactoside. Based on the RT-qPCR detection, CaGal-9 was ubiquitously expressed at mRNA level in various tested tissues, and predominately expressed in spleen. Upon Aeromonas hydrophila and poly I: C challenge, the expressions of CaGal-9 were remarkably up-regulated in liver, spleen, kidney and head kidney in a time-depended manner. The recombinant CaGal-9 (rCaGal-9), purified from Escherichia coli BL21 (DE3), exhibited strong binding ability with lipopolysaccharide (LPS), peptidoglycan (PGN) and β-Glucan, as well as the examined microorganisms including fungus, Gram-negative bacteria, and Gram-positive bacteria. With regard to the agglutinating activity of rCaGal-9, it could agglutinate erythrocytes of rabbit and crucian carp, and the examined microorganisms. Taken together, in this study, it was suggested that CaGal-9 could play an important role in immune defense against pathogenic microorganisms in C. auratus , which functions as an important PRR to recognize PAMPs and agglutinate pathogenic microorganisms. • A novel galectin-9 CaGal-9 was characterized in Carassius auratus. • CaGal-9 mRNA expressions were obviously up-regulated after pathogen challenges. • Recombinant CaGal-9 exhibited binding ability with LPS, PGN and β-Glucan. • Recombinant CaGal-9 could agglutinate erythrocytes and microorganism. • Recombinant CaGal-9 exhibited binding ability with seven kinds of microorganism. [ABSTRACT FROM AUTHOR]