Zinc finger protein 365 is a new maternal LPS-binding protein that defends zebrafish embryos against gram-negative bacterial infections

Zinc finger protein 365 (ZNF365) is widespread in animals, but its function and mechanism remains poorly defined. Here we clearly demonstrate that zebrafish ZNF365 is a newly identified LPS-binding protein capable of interacting with the gram-negative bacteria Escherichia coli, Vibrio anguillarum, and Aeromonas hydrophila, and functions as an antibacterial effector molecule capable of directly killing the bacteria. We also reveal that N-terminal residues 30-55 consisting of the ZnF_C2H2 domain are indispensable for ZNF365 antimicrobial activity. Importantly, microinjection of recombinant ZNF365 into early embryos significantly enhanced the resistance of the embryos against pathogenic A. hydrophila challenge, whereas down-regulation of ZNF365 by injection of znf365 morpholino into embryos considerably lowered their resistance against A. hydrophila challenge. Furthermore, the N-terminal peptide Z(30-55) with in vitro antibacterial activity also promoted the resistance of embryos against A. hydrophila, but the peptide Z(56-345) without in vitro antibacterial activity did not. Collectively, these results indicate that ZNF365 is a maternal LPS-binding protein that can protect the early embryos of zebrafish against pathogenic attacks, a novel role to be assigned to ZNF365 proteins. This work also provides new insights into the immunologic function of the zinc finger proteins that are widely distributed in various animals.