A single-CRD C-type lectin (CgCLec-3) with novel DIN motif exhibits versatile immune functions in Crassostrea gigas

• Published in: Fish & Shellfish Immunology
• Main Authors: Song, Xiaorui, Xin, Xiaoyu, Wang, Hao, Li, Hui, Zhang, Huan, Jia, Zhihao, Liu, Conghui, Jiang, Shuai, Wang, Lingling, Song, Linsheng
• Format: Report
• Language: English
• Published: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD 2019
• Subjects: Crassostrea gigas; C-type lectin; DIN motif; PAMP binding; Agglutination; Antibacterial activity; Fisheries; Immunology; Marine & Freshwater Biology; Veterinary Sciences; Pacific; Pacific oyster
• Online Access: http://ir.qdio.ac.cn/handle/337002/162720; http://ir.qdio.ac.cn/handle/337002/162721; https://doi.org/10.1016/j.fsi.2019.07.001

C-type lectins (CTLs), as important pattern recognition receptors (PRRs), are a superfamily of Ca2+-dependent carbohydrate-recognition proteins which participate in nonself-recognition and eliminating pathogens. In the present study, a novel CTL (designated as CgCLec-3) was identified from the Pacific oyster Crassostrea gigas. There was only one carbohydrate-recognition domain (CRD) of 151 amino acid residues within the deduced amino acid sequence of CgCLec-3. The deduced amino acid sequence of CgCLec-3 CRD shared low homology with the CRDs of other CTLs in oyster with the identities ranging from 12% to 22%. A novel DIN motif was found in Ca2+-binding site 2 of CgCLec-3. The relative expression level of CgCLec-3 in hemocytes was up-regulated significantly after the stimulations of bacteria and Pathogen Associated Molecular Patterns (PAMPs). Irnmunohistochemistry assay showed that CgCLec-3 protein was mainly distributed in gill and mantle, less in gonad, and could not be detected in adductor muscle and hepatopancreas. The recombinant protein (rCgCLec-3) could bind lipopolysaccharide (LPS), mannose (MAN) and peptidoglycan (PGN), but not poly (I:C). rCgCLec-3 odhibited strong binding ability to Vibrio anguillartun and V. splendidus, moderate binding activities to Escherichia colt, Pichia pastoris and Yatrowia lipotica, weak binding affinity to Staphylococcus aureus and Mictvcoccus luteus. rCgCLec-3 could agglutinate microorganisms, in a Ca2+-dependent manner and its activity to agglutinate V. splendidus was remarkably higher than that to agglutinate E. coli, S. aureus and P. pastoris. The phagocytic activity of oyster hemocytes was significantly enhanced after incubation with rCgCLec-3. rCgCLec-3 also exhibited antibacterial activity against E. coli and S. aureus. The results clearly suggested that CgCLec-3 in Pacific oyster C. gigas not only served as a PRR involved in the PAMPs recognition and microbes binding, but also functioned as an immune effector participating in the clearance of invaders.