Identification of ribosomal protein L30 as an uncharacterized antimicrobial protein

Several ribosomal proteins have been shown to adopt for an antimicrobial function as antimicrobial proteins (AMPs). However, information as such is rather limited and their mode of action remains ill-defined. Here we demonstrated that amphioxus RPL30, BjRPL30, was a previously uncharacterized AMP, which was not only capable of binding Gram-negative and Gram-positive bacteria via interaction with LPS, LTA and PGN but also capable of killing the bacteria. We also showed that the residues positioned at 2-46 formed the core region for the antimicrobial activity of BjRPL30. Notably, both the hydrophobic ratio and net charge as well as 3D structures of the residues corresponding to BjRPL302-27 and BjRPL3023-46 from both eukaryotic and prokaryotic RPL30 proteins were closely similar to those of BjRPL302-27 and BjRPL3023-46, suggesting the antibacterial activity of RPL30 was highly conserved. This was further corroborated by the fact that the synthesized counterparts human RPL5-30 and RPL26-49 also had antibacterial activity. We show that the recombinant protein BjRPL30 executes antimicrobial function in vitro by a kind of membranolytic action including interaction with bacterial membrane through LPS, LTA and PGN as well as induction of membrane depolarization. Finally, we found that neither BjRPL30 nor its truncated form BjRPL302-27 and BjRPL3023-46 had hemolytic activity towards human red blood cells, making them promising lead molecules for the design of novel AMPs against bacteria. Altogether, these indicated that RPL30 is a member of AMP which has ancient origin and is highly conserve throughout evolution.