Identification and expression of complement component C8α, C8β and C8γ gene in half-smooth tongue sole (Cynoglossus semilaevis) and C8α recombinant protein antibacterial activity analysis

Complement component C8, which mediates membrane attack complex formation and bacterial lysis, plays important roles in the complement system. The cDNA sequences of the C8 alpha, C8 beta and C8 gamma genes were cloned from half-smooth tongue sole (Cynoglossus semilaevis). Full-length cDNA of CsC8 alpha (C8 alpha of C. semilaevis), CsC8 beta and CsC8 gamma was 1990, 2219 and 886 bp, respectively, which contained open reading frames of 1797, 1749 and 666 bp, encoding 598, 582 and 221 amino acids, respectively. The deduced proteins of CsC8 alpha, CsC8 beta and CsC8 gamma showed the closest amino acid similarity to C8 alpha (73%) of Siniperca chuatsi, C8 beta (76%) of Oryzias latipes and C8 gamma (72%) of Takifugu rubripes, respectively. The highest expression level of CsC8 alpha, CsC8 beta and CsC8 gamma among the 13 normal tissues was observed in liver tissue, followed by much lower levels in other tissues. After infection with Vibrio anguillarum, CsC8 alpha, CsC8 beta and CsC8 gamma were significantly up-regulated in all of the detected tissues, including the intestine, liver, gill, head kidney, blood and spleen. Then, a recombinant expression plasmid was constructed, and the recombinant CsC8 alpha protein was expressed in GS115 pichia pastoris yeast. Furthermore, to investigate the biological functions of recombinant CsC8 alpha, an antibacterial assay was performed, and the results showed that recombinant CsC8 alpha obviously inhibited growth of V. anguillarum, Edwardsiella tarda and Vibrio parahaemolyticus. Taken together, these results suggest that CsC8 alpha, CsC8 beta and CsC8 gamma may play important roles in the immune defense of C. semilaevis.