Identification and functional characterization of first alpha-2-macroglobulin in sea cucumbers

The broad-spectrum protease inhibitor alpha-2-macroglobulin (M-2) is widely found in vertebrates and invertebrates. However, no research regarding M-2 has been described in sea cucumbers to date. In this study, the first sea cucumber M-2 named Stm(2)M was identified from Stichopus monotuberculatus, a tropical species with high edible and economic values in Southern China. The Stm(2)M cDNA is 5276bp in length, containing a 5-untranslated region (UTR) of 279bp, a 3-UTR of 344bp and an open reading frame of 4653bp that encodes a protein of 1550 amino acids. The Stm(2)M possesses all the three characteristics of known M-2 proteins, including the bait region domain, thioester domain and receptor-binding domain. Higher levels of mRNA expression were noticed in intestine, respiratory tree, coelomocytes and tentacle of S.monotuberculatus. Transcriptional expression of Stm(2)M showed the strongest response to lipopolysaccharides (LPS, 8.19-fold up-regulation) after 6h post-challenge in coelomocytes. In addition, the M-2 activity was detected in S.monotuberculatus and protein activity of M-2 increased remarkably at 6h after LPS stimulation. As a whole, this study indicated that Stm(2)M is an important immune-related molecule, and the study on functions of Stm(2)M may provide some new and valuable ideas for preventing and controlling diseases of cultured sea cucumbers.