Abstract
AbstractAlpha‐2‐macroglobulin (A2M) is essential for hosts defending against pathogen infections. In this study, two distinct A2Ms were identified from sea cucumbers Stichopus monotuberculatus and Holothuria atra, which belong to different genera in the Phylum Echinodermata, and named StmA2M and HaA2M, respectively. Structural analysis of StmA2M and HaA2M revealed that all contain the bait region domain, thioester domain, and receptor‐binding domain. Phylogenetic analysis indicated that StmA2M and HaA2M all belong to the echinoderm A2Ms. The cleavage site RXXR and the catalytic histidine residue for complement component C3 were found in StmA2M and HaA2M. Compared with human A2M, the three‐dimensional structures of StmA2M and HaA2M were more similar to that of common carp A2M. Both StmA2M and HaA2M showed the strongest response at transcriptional levels to lipopolysaccharide (LPS) at 12 h and polyriboinosinic polyribocytidylic acid [Poly (I: C)] at 24 h, respectively. Activity of StmA2M showed the strongest response to Poly (I: C) at 6 h, while the strongest change of HaA2M activity was induced by LPS at 24 h. The differential mRNA expression and enzyme activity levels suggested that A2M in sea cucumbers might be involved in different immune responses to LPS or Poly (I: C) challenge.
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