title: Discovery, structural characterization and functional analysis of alpha-2-macroglobulin, a novel immune-related molecule from Holothuria atra.
abstract: The non-specific protease inhibitor alpha-2-macroglobulin (A2M) is a key macromolecular glycoprotein that involved in host immune defense against pathogens in vertebrates and invertebrates. However, no research regarding A2M has been developed in echinoderms to date. In this study, the full-length cDNA of A2M was cloned from the sea cucumber (Holothuria atra), which is a tropical species widely distributed along the coasts of the South China Sea and designated HaA2M. HaA2M possesses all three conserved functional domains of known A2M proteins, including the bait region domain, thioester domain and receptor-binding domain. Compared to fish and shrimp A2Ms, the histidine residue from the catalytical regions is well conserved in HaA2M. HaA2M mRNA was predominantly expressed in coelomocytes and, to a lesser extent, in the body wall, intestine and respiratory tree. A2M activity was detected in the coelomic fluids of H. atra. The mRNA expression and activity levels were investigated in the major immune tissues and coelomic fluids of H. atra after challenge with inactivated Vibrio alginolyticus or polyriboinosinic polyribocytidylic acid [Poly (I: C)]. RNA interference (RNAi)-mediated knockdown of HaA2M resulted in a significant reduction of HaA2M gene transcript level (86%). RNAi-mediated silencing of HaA2M gene significantly decreased the A2M activity (38%) and increased the number of viable bacteria (2.8-fold) in the coelomic fluids of H. atra infected by V. alginolyticus. Our study, as a whole, supplied the evidences for HaA2M as an immune-relevant molecule and it might have multiple functions in the innate immune system of H. atra.
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China; University of Chinese Academy of Sciences, Beijing 100049, PR China. Electronic address: qianjing198722@126.com.
authors.forename: Jing
authors.initials: J
authors.lastname: Qian
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, PR China. Electronic address: rosemary166@sina.com.
authors.forename: Chunhua
authors.initials: C
authors.lastname: Ren
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China. Electronic address: jianjunxia@scsio.ac.cn.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Xia
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, PR China. Electronic address: chan1010@scsio.ac.cn.
authors.forename: Ting
authors.initials: T
authors.lastname: Chen
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China. Electronic address: yuzh@scsio.ac.cn.
authors.forename: Zonghe
authors.initials: Z
authors.lastname: Yu
authors.affiliation: CAS Key Laboratory of Tropical Marine Bio-resources and Ecology(LMB), Guangdong Provincial Key Laboratory of Applied Marine Biology (LAMB), South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301, PR China; South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, PR China. Electronic address: cqhu@scsio.ac.cn.
authors.forename: Chaoqun
authors.initials: C
authors.lastname: Hu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001826:Body Fluids / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA; D020868:Gene Silencing; D047332:Holothuria / Q000276:immunology*; D006801:Humans; D008969:Molecular Sequence Data; D010802:Phylogeny; D011487:Protein Conformation; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000235:genetics*
chemical_list: D000511:alpha-Macroglobulins; D004247:DNA
keywords: Alpha-2-macroglobulin; Holothuria atra; Immune defense; RNA interference; Tissue distribution; Transcriptional expression