Sequential rescue and repair of stalled and damaged ribosome by bacterial PrfH and RtcB.

RtcB is involved in transfer RNA (tRNA) splicing in archaeal and eukaryotic organisms. However, most RtcBs are found in bacteria, whose tRNAs have no introns. Because tRNAs are the substrates of archaeal and eukaryotic RtcB, it is assumed that bacterial RtcBs are for repair of damaged tRNAs. Here, we show that a subset of bacterial RtcB, denoted RtcB2 herein, specifically repair ribosomal damage in the decoding center. To access the damage site for repair, however, the damaged 70S ribosome needs to be dismantled first, and this is accomplished by bacterial PrfH. Peptide-release assays revealed that PrfH is only active with the damaged 70S ribosome but not with the intact one. A 2.55-Å cryo-electron microscopy structure of PrfH in complex with the damaged 70S ribosome provides molecular insight into PrfH discriminating between the damaged and the intact ribosomes via specific recognition of the cleaved 3'-terminal nucleotide. RNA repair assays demonstrated that RtcB2 efficiently repairs the damaged 30S ribosomal subunit but not the damaged tRNAs. Cell-based assays showed that the RtcB2-PrfH pair reverse the damage inflicted by ribosome-specific ribotoxins in vivo. Thus, our combined biochemical, structural, and cell-based studies have uncovered a bacterial defense system specifically evolved to reverse the lethal ribosomal damage in the decoding center for cell survival.

[Regulatory effect of the lipid metabolic pathways of TMAO, FMO3 and FXR on compound stress-induced ED in rats and mechanisms of Yimusake intervention].

OBJECTIVE: To study of the regulatory effects of the lipid metabolic pathways of trimethylamine-N-oxide (TMAO), flavin-containingmonooxidase 3 (FMO3) and farnesoid X receptor (FXR) on compound stress-induced ED (CSED) rats and the mechanisms of Yimusake Tablets (YMSK) intervention. METHODS: Based on the results of metabonomics analysis, we determined the concentration of TMAO in the serum of the rats in the normal control (n = 30), the CSED model control (n = 30) and the YMSK intervention group (intragastrical administration of YMSK at 250 mg/kg once daily for 2－3 weeks after modeling, n = 30) by nuclear magnetic resonance (NMR) spectroscopy test. We also detected the expressions of the FMO3, FXR1 and FXR2 proteins in the liver tissue of the three groups of rats by Western blot. RESULTS: The serum TMAO level was significantly elevated in the CSED model control compared with that in the normal control group (ï¼»46.64 ± 5.16ï¼½ vs ï¼»34.98 ± 3.69ï¼½ µg/mL, P < 0.01) but remarkably decreased after YMSK intervention (ï¼»39.63 ± 4.81ï¼½ µg/mL) in comparison with that in the CSED model control group (P < 0.01). The rats in the CSED model control group, compared with the normal controls, showed significantly upregulated expressions of FMO3 (1.75 ± 0.90 vs 0.86 ± 0.62, P < 0.01),FXR1 (1.29 ± 0.38 vs 0.78 ± 0.25, P < 0.01) and FXR2 in the liver tissue (1.90 ± 0.63 vs 0.42 ± 0.27, P < 0.01), but all the three expressions were markedly decreased after YMSK intervention (FMO3: 1.05 ± 0.38, P < 0.05; FXR1: 1.07 ± 0.42, P < 0.05; FXR2: 1.04 ± 0.46, P < 0.01) as compared with those in the CSED model control group. CONCLUSIONS: The lipid metabolic pathways of TMAO, FMO3 and FXR underwent significant changes in the rat model of compound stress-induced ED, which could be improved by YMSK intervention, suggesting that YMSK may play an important role in protecting erectile function by regulating the lipid metabolic pathways of TMAO, FMO3 and FXR.