Institute of Oceanography, Minjiang University, Fuzhou, Fujian, 350108, China.
State Key Laboratory Breeding Base of Marine Genetic Resources, Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, Fujian, 361005, China.
Comp Biochem Physiol B Biochem Mol Biol. 2019 Dec;238:110329. doi: 10.1016/j.cbpb.2019.110329. Epub 2019 Aug 25.
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 A-I（ApoA-I）在脂质转运中发挥重要作用，并在脊椎动物中具有抗菌活性。然而，ApoA-I 在无脊椎动物中的作用在很大程度上仍未得到探索。在这项研究中，从文昌鱼（Branchiostoma belcheri）中克隆出一种载脂蛋白 A-I 基因，命名为 BbApoA-I，其开放阅读框为 1466bp，编码 345 个氨基酸的多肽。预测的多肽显示出保守特征，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。定量实时 PCR 分析表明，BbApoA-I 在所有测试的组织中均有检测到，在肝盲囊中的表达量最高。在向标本中注射脂多糖后，BbApoA-I 的表达上调。在大肠杆菌表达系统中产生的重组 BbApoA-I 能够结合广泛的革兰氏阳性和革兰氏阴性细菌以及脂多糖和脂磷壁酸。此外，rBbApoA-I 表现出针对革兰氏阴性细菌的体外抗菌活性。这些结果表明，BbApoA-I 在文昌鱼中发挥了针对细菌感染的保护功能。
