Identification, expression analysis, and antibacterial activity of Apolipoprotein A-I from amphioxus (Branchiostoma belcheri).

Apolipoprotein A-I (ApoA-I) plays an important role in lipid transport and performs an antimicrobial activity in vertebrates. However, the role of ApoA-I in invertebrates remains largely unexplored. In this study, an ApoA-I gene named BbApoA-I having an open reading frame of 1466 bp and encoding a polypeptide of 345 amino acids was cloned from a cephalochordate (Branchiostoma belcheri). The predicted polypeptide revealed conserved features, including α-helical secondary structures and coiled-coil regions in known vertebrate ApoA-I sequences. Quantitative real-time PCR analysis indicated that BbApoA-I was detected in all of the tested tissues, and the highest expression was found in the hepatic cecum. The BbApoA-I expression was upregulated after the specimens were injected with lipopolysaccharide. Recombinant BbApoA-I produced in an E. coli expression system was able to bind to a wide range of Gram-positive and Gram-negative bacteria as well as lipopolysaccharide and lipoteichoic acid. In addition, rBbApoA-I exhibited in vitro antibacterial activity against Gram-negative bacteria. These results indicated that BbApoA-I performed a protective function against bacterial infection in amphioxus.