A novel LRR and Ig domain-containing protein could function as an immune effector in Crassostrea gigas

• Published in: Fish & Shellfish Immunology
• Main Authors: Wang, Xiudan, Zhao, Xiaoli, Yan, Chunyu, Jia, Zhihao, Lv, Zhao, Ma, Cuiping, Wang, Mengqiang
• Format: Report
• Language: English
• Published: ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD 2019
• Subjects: Crassostrea gigas; Leucine-rich repeat domain; Immunoglobulin domain; LRRIG; Pattern recognition receptor; Immune effector; Fisheries; Immunology; Marine & Freshwater Biology; Veterinary Sciences; LEUCINE-RICH REPEAT; SOLUBLE ADENYLYL-CYCLASE; ONLY PROTEINS; RECOGNITION; SUPERFAMILY; EXPRESSION; PATTERN; PHAGOCYTOSIS; MECHANISMS; COMPLEXITY; Psi
• Online Access: http://ir.qdio.ac.cn/handle/337002/161103; https://doi.org/10.1016/j.fsi.2019.03.003

A variety of combinations of leucine-rich repeat (LRR) and immunoglobulin-like (Ig) domains have been found and discovered in invertebrates and vertebrates, but the functions remain largely unexplored. In the present study, a novel LRR and Ig domain-containing protein (LRRIG), CgLRRIG-3, was identified and characterized from oyster Crassostrea gigas. It contained two typical LRR motifs, a LRRNT motif and an Ig domain and PSI-BALST and phylogeny analysis revealed that the sequence of CgLRRIG-3 was most related with leucine-rich repeat neuronal 1 proteins from vertebrate. Its mRNA transcripts were constitutively expressed in muscle, gill, hepatopancreas, mantle, gonad and hemocytes with the highest level in hepatopancreas. The mRNA expression level of CgLRRIG-3 in hemocytes could respond to the stimulations of variety PAMPs including lipopolysaccharide (LPS), peptidoglycan (PGN), glucan (GLU) and polyinosinic-polycytidylic acid (poly I:C). The recombinant proteins exhibited a wide PAMP binding repertoire to four typical PAMPs and could significantly induce the expression of CgTNF-1 and CgIL17-5 as well as increase phagocytosis in primary cultured oyster hemocytes. In hepatopancreas, CgLRRIG-3 was mainly distributed in the basolateral membrane of digestive tubule and the hemocoel sinusoid between the digestive tubules. And in hemocytes, the positive signal was mainly distributed in a special group of granulocytes. These results collectively indicated that CgLRRIG-3 could not only function as an immune effector.