Abstract:

Major histocompatibility complex (MHC) is a highly polymorphic molecule that plays an essential role in vertebrates' innate immune response. Specific primers were designed according to the reported MHCⅠα sequence of fish. Finally, the full-length MHCⅠα cDNA sequence of Megalobrama terminalis was obtained by RT-PCR and RACE. The cDNA sequence was named Mete-UAA and conducted bioinformatics analysis. The results showed that the Mete-UAA was 2 102 bp in length, containing 1 044 bp open reading frame, encoding 347 amino acids. The Mete-UAA encoded a hydrophilic protein that contains 16 amino acid signal peptides. It was localized on the cell membrane and had one N-glycosylation, three O-glycosylation, and 39 potential phosphorylation sites. The encoded MHCⅠα protein had a predicted relative molecular mass of 38 699.18 and an isoelectric point of 5.23. Amino acid sequence homology comparison showed that the homology of the Mete-UAA amino acid sequence was up to 75.79% with M. amblycephala (AEE87250) and 75.25% with Ctenopharyngodon idella (BAD01521) slightly lower than M. amblycephala (AEE87250). The Mete-UAA possessed the typical structural features of MHCⅠα, including a leader peptide, three extracellular domains, one transmembrane region, and one cytoplasmic region. The secondary structure analysis of the Mete-UAA protein showed that the proportions of the α-helix, β-turn, extended chain and random coil were 25.94%, 9.22%, 26.80%, and 38.04%, respectively. Based on the transcriptome analysis, expression of the MHCⅠα gene in M. terminalis infected with Aeromonas hydrophila showed an overall decreasing trend. In this study, the MHCⅠα gene was successfully cloned from the liver of M. terminalis. Its bioinformatics characteristics were analyzed, which would provide a theoretical basis for further research on the mechanism of MHCⅠα involved in regulating the innate immune response in M. terminalis.

Key words: Megalobrama terminalis, major histocompatibility complex, gene cloning, bioinformatic analysis