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 high... More
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.
