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

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