CgMpeg1a from oyster Crassostrea gigas destroys and eliminates Vibrio splendidus.

Macrophage-expressed gene 1 [Mpeg1/Perforin-2 (PRF2)] is an ancient metazoan protein belonging to the membrane attack complex/perforin (MACPF) branch of the MACPF/cholesterol dependent cytolysin (CDC) superfamily of pore-forming proteins (PFPs). However, the mechanism of Mpeg-mediated bacterial damage remains unclear in invertebrates. In the present study, a macrophage expressed gene was identified in Crassostrea gigas and designated as CgMpeg1a. The complete cDNA of CgMpeg1a is 2641 bp in length, containing an ORF of 1953 bp, which encodes a putative protein of 650 amino acids with a predicted 1-20 aa signal peptide and a MACPF domain at 140-339 aa. CgMpeg1a mRNA was detected in all the tested tissues. The mRNA expression levels of CgMpeg1a in hemocytes and gills increased significantly after Vibrio splendidus stimulation. The recombinant CgMpeg1a protein (rCgMpeg1a) could bind various bacteria. The number of damaged bacteria, antibacterial activity and the contents of K+, ALP and LDH in the bacterial supernatant were all enhanced after the incubation of bacteria with rCgMpeg1a. The results indicated that invertebrate Mpeg1 exerted cytotoxic function to destroy the invading pathogens.