Molecular cloning of the alpha subunit of complement component C8 (CpC8α) of whitespotted bamboo shark (Chiloscyllium plagiosum)

Complement-mediated cytolysis is the important effect of immune response, which results from the assembly of terminal complement components (C5b-9). Among them, alpha subunit of C8 (C8 alpha) is the first protein that traverses the lipid bilayer, and then initiates the recruitment of C9 molecules to form pore on target membranes. In this article, a full-length cDNA of C8 alpha (CpC8 alpha) is identified from the whitespotted bamboo shark (Chiloscyllium plagiosum) by RACE. The CpC8 alpha cDNA is 2183 bp in length, encoding a protein of 591 amino acids. The deduced CpC8 alpha exhibits 89%, 49% and 44% identity with nurse shark, frog and human orthologs, respectively. Sequence alignment indicates that the C8 alpha is well conserved during the evolution process from sharks to mammals, with the same modular architecture as well as the identical cysteine composition in the mature protein. Phylogenetic analysis places CpC8 alpha and nurse shark C8 alpha in cartilaginous fish clade, in parallel with the teleost taxa, to form the C8 alpha cluster with higher vertebrates. Hydrophobicity analysis also indicates a similar hydrophobicity of CpC8 alpha to mammals. Finally, expression analysis revealed CpC8 alpha transcripts were constitutively highly expressed in shark liver, with much less expression in other tissues. The well conserved structure and properties suggests an analogous function of CpC8 alpha to mammalian C8 alpha, though it remains to be confirmed by further study. (C) 2013 Elsevier Ltd. All rights reserved.