A pattern recognition receptor ficolin from Portunus trituberculatus (Ptficolin) regulating immune defense and hemolymph coagulation.

Ficolins, belonging to the fibrinogen-related protein superfamily, are important pattern recognition receptors in innate immunity. Here, a ficolin gene Ptficolin was characterized from the swimming crab Portunus trituberculatus. The completed cDNA sequence of Ptficolin encoded a signal peptide, a coiled-coil region and a fibrinogen-like domain but without the typical collagen region of vertebrate ficolins. Ptficolin showed higher expression in stomach and hepatopancreas, and presented a time-dependent response after pathogen challenge and injury stimulation. The recombinant Ptficolin (rPtficolin) could bind to various PAMPs and microorganisms, and agglutinate microorganisms and rabbit erythrocytes in a Ca2+-dependent manner, with strong binding ability to N -acetyl sugars. Meanwhile, rPtficolin promoted the hemocyte phagocytosis and clearance activity of Vibrio , while Ptficolin knockdown impaired the bacterial phagocytosis and clearance ability, suggesting the opsonin activity of Ptficolin. Knockdown of Ptficolin could downregulate the transcription of most complement-like genes and AMPs, but enhance the expression of most proPO system-related genes and key genes of Toll, IMD and JNK pathways. Moreover, knockdown of Ptficolin led to the increased hemolymph clotting time and the decreased expression of clotting-related genes. Our results indicate that Ptficolin could recognize and eliminate invading pathogens, and might be a prominent component in hemolymph coagulation of crab. • Ptficolin was a novel ficolin isolated from Portunus trituberculatus. • Ptficolin exhibited strong binding, agglutinating and antibacterial activity. • Ptficolin showed opsonic activity that promote phagocytosis and bacterial clearance. • Knockdown of Ptficolin downregulated the expression of complement-like genes, AMPs and clotting-related genes. • Ptficolin might be a prominent component in hemolymph coagulation of crab. [ABSTRACT FROM AUTHOR]