Ribosomal protein genes S23 and L35 from amphioxus Branchiostoma belcheri tsingtauense: identification and copy number

Identification and functional characterization of ribosomal protein S23 as a new member of antimicrobial protein

Previous studies show that some ribosomal proteins possess antimicrobial peptide (AMP) activity. However, information as such remains rather fragmentary and rather limited. We showed here for the first time that amphioxus RPS23, BjRPS23, was a previously uncharacterized AMP. It not only acted as a pattern recognition receptor, capable of identifying LPS, LTA and PGN, but also an effector, capable of killing the Gram-negative and -positive bacteria. We also showed that the residues positioned at 67-84 formed the core region for the antimicrobial activity of BjRPS23, and its orthologues Verrucomicrobia RPS12_68-85 and Thermotoga RPS12_65-82 similarly displayed some antibacterial activities. BjRPS23 functioned by a combined action of membranolytic mechanisms including interaction with bacterial membrane via LPS, LTA and PGN, and membrane depolarization. BjRPS23 also stimulated production of intracellular ROS in bacteria. Moreover, we demonstrated that RPS23 existed across widely separated taxa, and might play a universal role in protection against bacterial infection in different animals. In addition, we found that neither BjRPS23 nor its truncated form BjRPS23_67-84 were cytotoxic to mammalian cells, making them promising lead molecules for the design of novel peptide antibiotics against bacteria. Collectively, these indicate that RPS23 is a new member of AMP with ancient origin and high conservation.

60S ribosomal protein L35 regulates β-casein translational elongation and secretion in bovine mammary epithelial cells

60S ribosomal protein L35 (RPL35) is an important component of the 60S ribosomal subunit and has a role in protein translation and endoplasmic reticulum (ER) docking. However, few studies have investigated RPL35 in eukaryotes and much remains to be learned. Here, we analyzed the function of RPL35 in β-casein (CSN2) synthesis and secretion in bovine mammary epithelial cells (BMECs). We found that methionine (Met) could promote the expressions of CSN2 and RPL35. Analysis of overexpression and inhibition of RPL35 confirmed that it could mediate the Met signal and regulate CSN2 expression. The mechanism of CSN2 regulation by RPL35 was analyzed by coimmunoprecipitation (Co-IP), colocalization, fluorescence resonance energy transfer (FRET) and gene mutation. We found that RPL35 could control ribosome translational elongation during synthesis of CSN2 by interacting with eukaryotic translational elongation factor 2 (eEF2), and that eEF2 was the signaling molecule downstream of RPL35 controlling this process. RPL35 could also control the secretion of CSN2 by locating it to the ER. Taken together, these results revealed that, RPL35 was an important positive regulatory factor involving in the Met-mediated regulation of CSN2 translational elongation and secretion.

Verification, characterization and tissue-specific expression of UreG, a urease accessory protein gene, from the amphioxus Branchiostoma belcheri

UreG genes have been found in bacteria, fungi and plants but have not yet identified in animals, although a putative UreG-like gene has been documented in sea urchin. In the course of a large-scale sequencing of amphioxus gut cDNA library, we have identified a cDNA with high similarity to UreG genes. Both reverse transcription-polymerase chain reaction and nested polymerase chain reaction, as well as in situ hybridization histochemistry, verified that the cDNA represented an amphioxus UreG gene (AmphiUreG) rather than a microbial contaminant of the cDNA library. This is further supported by the presence of urease activity in amphioxus gut, gill and ovary. AmphiUreG encodes a deduced protein of 200 amino acid residues including a highly conserved P-loop, bearing approximately 46%-49%, 44%-48%, and 29%-37% similarity to fungal, plant and bacterial UreG proteins, respectively. It shows a tissue-specific expression pattern in amphioxus, and is especially abundant in the digestive system. This is the first UreG gene identified in animal species.