Shrimp invertebrate lysozyme i-lyz: Gene structure, molecular model and response of c and i lysozymes to lipopolysaccharide (LPS)

The invertebrate lysozyme ( i-lyz or destabilase) is present in shrimp. This protein may have a function as a peptidoglycan-breaking enzyme and as a peptidase. Shrimp is commonly infected with Vibrio sp., a Gram-negative bacteria, and it is known that the c-lyz (similar to chicken lysozyme) is active against these bacteria. To further understand the regulation of lysozymes, we determined the gene sequence and modeled the protein structure of i-lyz. In addition, the expression of i-lyz and c-lyz in response to lipopolysaccharide (LPS) was studied. The shrimp i-lyz gene is interrupted by two introns with canonical splice junctions. The expression of the shrimp i-lyz was transiently down-regulated after LPS injection followed by induction after 6 h in hepatopancreas. In contrast, c-lyz was up-regulated in hepatopancreas 4 h post-injection and slightly down-regulated in gills. The L. vannamei i-lyz does not contain the catalytic residues for muramidase (glycohydrolase) neither isopeptidase activities; however, it is known that the antibacterial activity does not solely rely on the enzymatic activity of the protein. The study of invertebrate lysozyme will increase our understanding of the regulatory process of the defense mechanisms. ► L. vannamei i-lyz lacks the catalytic residues for muramidase and isopeptidase activities. ► i-lyz gene has two introns, and the molecular modeling suggests that it only binds. ► i-lyz mRNA was down-regulated after LPS after 6 h in hepatopancreas. ► c-lyz was up-regulated in hepatopancreas 4 h post-injection and then reduced in gills. ► These data suggests that hepatopancreas has a role in immune response to LPS in shrimp.