Characterization of a group D anti-lipopolysaccharide factor (ALF) involved in anti-Vibrio response in Penaeus monodon.

Antimicrobial peptides (AMPs) are an essential component of innate immunity of invertebrates. Anti-lipopolysaccharide factor (ALF)， as a main type of AMPs in crustaceans， attends in the disease prevention in general. In this research， a novel Group D ALF was identified and characterized from Penaeus monodon， named PenmonALF8. It was an anionic peptide， with both the full-length peptide and lipopolysaccharide binding domain (LBD) a low isoelectric point. PenmonALF8， composed of a signal peptide of 26 amino acids and a mature peptide of 98 amino acids， probably contained three alpha helixes and four beta sheets. Moreover， PenmonALF8 was detected in all tested tissues of P. monodon， and the expression level in hemocyte and intestine was relatively high. When challenged by Vibrio parahaemolyticus， PenmonALF8 showed 30-100 times higher expression level in all the tissues except in hemocyte and intestine， indicating that PenmonALF8 played a very important role in the immune response of P. monodon. By fusing to a SUMO protein， PenmonALF8 was successfully over-expressed in E. coli and purified by affinity chromatography. Additionally， the reconstituted PenmonALF8 and its LBD region displayed modest antimicrobial activity. This is the first research about the Group D ALF in P. monodon， which provides more information for humoral immunity study of shrimps.