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.

载脂蛋白AI（ApoA-I）在脂质运输中起重要作用，并在脊椎动物中发挥抗菌活性。但是，ApoA-I在无脊椎动物中的作用仍未开发。在这项研究中，从头孢霉（Belcheriostoma belcheri）克隆了一个ApoA-I基因，名为BbApoA-I，其开放阅读框为1466 bp，编码345个氨基酸的多肽。）。预测的多肽揭示了保守的特征，包括已知脊椎动物ApoA-I序列中的α-螺旋二级结构和卷曲螺旋区域。实时定量PCR分析表明，在所有测试组织中均检测到BbApoA-I，并且在肝盲肠中发现了最高的表达。在标本中注入脂多糖后，BbApoA-I表达上调。在大肠杆菌表达系统中产生的重组BbApoA-I能够与多种革兰氏阳性和革兰氏阴性细菌以及脂多糖和脂磷壁酸结合。此外，rBbApoA-I在体外表现出对革兰氏阴性菌具有抗菌活性。这些结果表明，BbApoA-1对双歧杆菌具有抗细菌感染的保护功能。