Abstract
Conventional role of ribosomal proteins is ribosome assembly and protein translation, but some ribosomal proteins also show antimicrobial peptide (AMP) activity, though their mode of action remains ill-defined. Here we demonstrated for the first time that amphioxus RPS15, BjRPS15, was a previously uncharacterized AMP, which was not only capable of identifying Gram-negative and -positive bacteria via interaction with LPS and LTA but also capable of killing the bacteria. We also showed that both the sequence and 3D structure of RPS15 and its prokaryotic homologs were highly conserved, suggesting its antibacterial activity is universal across widely separated taxa. Actually this was supported by the facts that the residues positioned at 45–67 formed the core region for the antimicrobial activity of BjRPS15, and its prokaryotic counterparts, including Nitrospirae RPS1933−55, Aquificae RPS1933−55 and P. syringae RPS1950-72, similarly displayed antibacterial activities. BjRPS15 functioned by both interaction with bacterial surface via LPS and LTA and membrane depolarization as well as induction of intracellular ROS. Moreover, we showed that RPS15 existed extracellularly in amphioxus, shrimp, zebrafish and mice, hinting it may play a critical role in systematic immunity in different animals. In addition, we found that neither BjRPS15 nor its truncated form BjRPS1545–67 were toxic to mammalian cells, making them promising lead molecules for the design of novel AMPs against bacteria. Collectively, these indicate that RPS15 is a new member of AMP with ancient origin and high conservation throughout evolution.
Highlights
The ribosome is an organelle within the cytoplasm of living cells that is composed of proteins and ribosomal RNAs, serving as the site for assembly of polypeptides encoded by messenger RNAs
We 51 demonstrated for the first time that amphioxus ribosomal protein 15 was a novel antibacterial protein, capable of recognizing Gram-negative and -positive bacteria as well as killing them. It killed the bacteria by a combined mode of action of disrupting bacterial membrane integrity and inducing radical oxygen species production. We showed that both 56 eukaryotic ribosomal protein 15 and its prokaryotic counterpart ribosomal 57 protein 19 possessed antibacterial activity, indicating that the antibacterial 58 property is universal for this family of molecules
We found 59 that ribosomal protein 15 was present in the circulation system of various 60 animals including shrimp, amphioxus, zebrafish and mice, suggesting it may physiologically play a key role in systematic immunity
Summary
The ribosome is an organelle within the cytoplasm of living cells that is composed of proteins and ribosomal RNAs (rRNAs), serving as the site for assembly of polypeptides encoded by messenger RNAs (mRNAs). Ribosomes are found in both prokaryotic and eukaryotic cells. In both types of cells, ribosomes are composed of two subunits, one large and one small [1,2]. Each subunit has its own mix of proteins and rRNAs. The small and large subunits of eukaryotes are called 40S and 60S, respectively, while those of prokaryotes called 30S and 50S, separately. Ribosomal protein S15 (RPS15) is a component of the 40S subunit of eukaryotes, while its homolog in prokaryotes is S19 (RPS19) of the 30S subunit [3]
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