Characterization and function analysis of an anti-lipopolysaccharide factor (ALF) from the Chinese shrimp Fenneropenaeus chinensis

• An ALF isoform (FcALF2) highly expressed in the lymphoid organ (Oka) of the shrimp was characterized.
• Synthetic LPS-binding domain of FcALF2 showed antibacterial and antiviral activities.
• The antibacterial activities of the synthetic peptides were apparently enhanced after increasing basic amino acids.

Anti-lipopolysaccharide factor (ALF) is one of the widely-studied antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity and antiviral property. Previous studies show the existence of multiform of ALFs in crustacean which are important for immunity of the animals. In the present study, we characterized one isoform of ALF from the Chinese shrimp Fenneropenaeus chinensis (FcALF2). Tissue distribution analysis revealed that FcALF2 showed the highest expression level in the lymphoid organ (Oka) of the shrimp. The expression level of FcALF2 in shrimp was significantly up-regulated when they were injected with Micrococcus lysodeikticus and Vibrio anguillarum. A peptide corresponding to the LPS-binding domain of FcALF2 (FcALF2-LBD) was synthesized to analyze its antimicrobial activities. Data demonstrated that FcALF2-LBD possessed strong antibacterial activity against Gram-positive bacteria Micrococcus luteus and M.lysodeikticus with MIC ranges of 2–4 μM and 1–2 μM respectively and significant inhibition activity against white spot syndrome virus (WSSV). The antibacterial activities of the sequence modified peptides (FcALF2-LBDb, FcALF2-LBDv) were apparently enhanced and broadened after the amount of basic amino acids was increased in the synthetic LPS-binding domain. These data provide more insights into understanding the function of LPS-binding domain of ALF and the role of ALF in shrimp immunity.