Comparative Characterization of Sequence Structure, Gene Expression, and Enzyme Activity of Alpha-2-macroglobulin between Stichopus monotuberculatus (Stichopodidae) and Holothuria atra (Holothuriidae)

摘要

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