Bactericidal permeability-increasing protein/LPS-binding protein (BPI/LBP) enhances resistance of golden pompano Trachinotus ovatus against bacterial infection

Antimicrobial peptides are crucial components of innate immunity against microbial invasions. As a kind of antimicrobial peptides, bactericidal permeability-increasing protein (BPI)/lipopolysaccharide-binding protein (LBP) play vital roles in defending the host against gram-negative bacteria. In the current study, a novel BPI/LBP from Trachinotus ovatus (TroBPI/LBP) was characterized. The full length of TroBPI/LBP cDNA sequence is 1434 bp, which contained 477 amino acids. Multiple amino acid alignments of TroBPI/LBP shows 34.07%-84.49% identity with other fish BPI/LBP. Similar to other BPI/LBP, TroBPI/LBP also possesses an N-terminal signal peptide, a BPI/LBP/CETP N-terminal domain, and a BPI/LBP/CETP C-terminal domain. In vitro, the recombinant protein of TroBPI/LBP showed effective bacterial depression activity and binding activity to gram-negative bacteria. In vivo, TroBPI/LBP was constitutively expressed in tested tissues, and the highest expression level was in liver. Following Vibrio alginolyticus stimulation, the mRNA expression of TroBPI/LBP was significantly upregulated in immune-related tissues, and peaked at 12 h post-infection, which confirmed that TroBPI/LBP was highly sensitive to V. alginolyticus stimuli. Furthermore, functional analyses showed that the overexpression of TroBPI/LBP could enhance the ability of fish to against V. alginolyticus infection, and the knockdown of TroBPI/LBP significantly diminished bacterial clearance capacity post-infection. Therefore, these results suggest that TroBPI/LBP may play an important role in host defense against bacterial infection.