Abstract:Exopalaemon carinicauda is one of most commercially important shrimps in China Sea due to its advantage in reproduction, longer growing seasons, and ecological flexibility. However, a variety of shrimp diseases have become an increasingly serious issue that lead to economic loss. E. carinicauda relies on the innate immunity to fight against invading pathogens. Alpha2-Macrogloblin (α2M) is an inhibitor of diverse proteases ubiquitous in animals. Alpha2M enfolds the target proteases and block their interactions. Therefore α2M plays an important part in avoiding the deleterious effects of its active components. Based on the EST sequence from a cDNA library of E. carinicauda hemocyte，we cloned the cDNA of alpha2-macrogloblin of E. carinicauda (namely Ecα2M) using rapid amplification of cDNA ends (RACE). The Ecα2M cDNA was 4823 bp in length, which contained an open reading frame (ORF) of 4413 bp, a 64 bp 5 untranslated region, and a 346 bp 3 untranslated region. The open reading frame encoded an N-terminal signal sequence of 23 residues, and a mature protein consisting of 1470 amino acids. The molecular mass of this protein was 163.0 kDa and the estimated pI was 5.03. Homology analysis revealed that the amino acid sequence of Ecα2M was highly similar to its homologs in other crustaceans. The similarity of Ecα2M was 80% between E. carinicauda and Macrobrachium rosenbergii. We also analyzed the expression of Ecα2M in different tissues with quantitative real-time PCR. Ecα2M was detected in all tested tissues of E. carinicauda, including hemocytes, gill, hepatopancreas, muscles, ovary, intestine, stomach and eyestalk, and the expression was the highest in hemocytes. After challenged with Vibrio anguillarum and white spot syndrome virus (WSSV), the expression of Ecα2M was up-regulated in hemocytes and hepatopancreas of E. carinicauda. Our results suggested that Ecα2M might play an important role in the prawn immune response.
