Mannose-binding C-type lectin from Procambarus clarkii exhibited antimicrobial activity to mediate crayfish innate immunity

Mannose-binding lectin (MBL), which is a member of the C-type lectin (CTL) family, plays crucial roles in nonself recognition and the clearance of invading microorganisms. In this study, an MBL (designated as PcMBL) was cloned and characterized from the crayfish Procambarus clarkii. PcMBL cDNA consisted of 816 bp encoding a protein with 271 amino acid residues. The deduced PcMBL contained a signal peptide, three low-complexity regions, and a carbohydrate-recognition domain, as found in most CTLs. The mRNA encoding PcMBL was detected in all the examined tissues. PcMBL expression in hemocytes and intestines was significantly upregulated after stimulation with Vibrio parahaemolyticus and Staphylococcus aureus. RNA interference studies revealed that PcMBL silencing remarkably downregulated the transcription of five antimicrobial peptide genes, namely, Antilipopolysaccharide factor 1 (ALF-1), ALF-4, ALF-10, Crustin 1 (Crus-1), and Crus-4. Recombinant PcMBL protein was used for the functional analysis. The results showed that rPcMBL had the capacity to bind to all seven tested microorganisms and three carbohydrates. rPcMBL facilitated the clearance of V. parahaemolyticus and S. aureus and inhibited the formation of biofilms and growth of the two bacteria. In addition, rPcMBL could reduce the mortality of crayfish infected with V. parahaemolyticus or S. aureus. All these results suggest that PcMBL may be involved in immune recognition and pattern elimination in the innate immunity of P. clarkii.