Conserved structural complement component C3 in miiuy croaker Miichthys miiuy and their involvement in pathogenic bacteria induced immunity.

Complement component C3 is a key protein in the complement system whose activation is essential for all the important functions performed by this system. In this study, the complete C3 cDNA sequence was isolated from the miiuy croaker (Miichthys miiuy), which was high similarity to other complement C3. In this study, we report the primary sequence, the tissue expression profile, the polypeptide domain architecture and the phylogenetic analysis of miiuy croaker C3 gene. Rapid amplification of the cDNA ends (RACE) yielded the full open reading frame of this protein (4974 bp), and subsequent analysis indicated that the M. miiuy C3 gene encoded a protein of 1657 amino acids. The deduced amino acid sequence showed that M. miiuy C3 has conserved residues and domains known to be critical for C3 function. Phylogenetic analysis showed that miiuy croaker was most closely related to Epinephelus coioides. Expression analysis showed that C3 was expressed differentially in miiuy croaker tissues, while liver was the main source of C3 expression. Infection of miiuy croaker with Vibrio anguillarum resulted in significant changes expression of C3 gene in the immune-related tissues. These results showed that C3 gene might play an important role in immune mechanisms.