Cloning and characterization of a shrimp ML superfamily protein

ML superfamily proteins, including MD-1, MD-2, Niemann-Pick type C2 (Npc2) protein, GM2 activator protein, phosphatidylinositol/phosphatidylglycerol transfer protein (PG/PI-TP) and mite allergen Der p 2, bind to specific lipids and play important roles in lipid-recognition and metabolism. Among these ML (MD-2-related lipid-recognition) proteins, MD-2 is essential for lipopolysaccharide (LPS) signaling and the following secretion of proinflammatory factors. In this report, we identified the cDNA and gene of an ML protein from an important white shrimp Litopenaeus vannamei and named it LvML. The gene consists of four exons and three introns. The putative LvML contains 6 cysteines which may form 3 disulfide bonds that are conserved in ML proteins. Reverse transcription PCR analysis showed that in the examined tissues LvML mRNA is only expressed in the hepatopancreas, while not in hemocytes, eyestalk, gill, heart, stomach, intestine, nerve core, muscle or pyloric caecum. Its expression is positively regulated after injection of LPS. Then enzyme-linked immunosorbent assay showed that the recombinant LvML possessed activity of binding to LPS, and that the binding was inhibited by pre-incubation with LPS. We suggested that the LvML may play roles in the shrimp innate immunity.