Giant Triton Snail Charonia tritonis Macrophage-Expressed Gene 1 Protein Ct-Mpeg1: Molecular Identification, Expression Analysis, and Antimicrobial Activity

Macrophage-expressed gene 1 proteins (Mpeg1/Perforin-2 (PRF2)) are a family of pore-forming proteins (PFPs) which can form pores and destroy the cell membrane of invading pathogens. However, little information is available regarding the function of Mpeg1 in the giant triton snail Charonia tritonis. In this study, a homolog of Mpeg1 (Ct-Mpeg1) was identified in C. tritonis. The predicted protein of Ct-Mpeg1 contains several structural features known in Mpegs, including a membrane attack complex/perforin (MACPF) domain and single transmembrane region. The Ct-Mpeg1 gene was constitutively expressed in almost all tissues examined except in the proboscis, with the highest expression level observed in the mantle. As a typical pore-forming protein, Ct-Mpeg1 has antibacterial activities against Vibrio (including Vibrio alginolyticus and Vibrio parahaemolyticus). In addition, rCt-Mpeg1 challenge to V. alginolyticus represses the expression of most outer membrane protein synthesis-related genes and genes involved in the TCA cycle pathway, which will lead to reduced outer membrane protein synthesis and less energy capacity. This is the first report to characterize the macrophage-expressed gene 1 protein in C. tritonis, and these results suggest that macrophage-expressed gene 1 protein Ct-Mpeg1 is an important immune molecule of C. tritonis that is involved in the bacterial infection resistance of Vibrio, and this study may provide crucial basic data for the understanding of the innate immunity system of C. tritonis.