Role of VirB1-89K in bacterial virulence
To assess the role of VirB1-89K in bacterial virulence, an isogenic knockout mutant of virB1-89K (ΔvirB1-89K) constructed in our previous work p38 MAPK activation and its complementary strain CΔvirB1-89K were subjected to experimental infection of mice . We found that group of mice infected with the wild-type strain 05ZYH33 developed obvious clinical signs of S. suis infection, including rough hair coat, weight loss, depression, shivering, and suppuration of the eyes. There were no survivors at 12 hours post-infection (Figure 5). However, mice in the ΔvirB1-89K mutant group were all alive at 12 hours post-infection and had a survival rate of 70% at the experimental end point of 7 days. When mice were challenged with the complemented strain, CΔvirB1-89K, data
similar to those obtained with the wild-type strain were observed. In the THY control group, all mice survived without any disease symptoms during the Fludarabine in vivo entire experiment. These results strongly indicated that VirB1-89K is involved in the pathogenesis of Chinese epidemic S. suis 2 strains. Figure 5 Survival curves of mice infected with S. suis 05ZYH33, the Δ virB1 – 89K mutant, the complemented strain these CΔ virB1 – 89K , and the THY medium. Mice (10 per group) were inoculated intraperitoneally with 108 CFU bacteria. Results shown are representative of three independent experiments. Discussion T4SSs are versatile devices that are found in many bacterial pathogens and secrete a wide variety of substrates, from single protein to protein-protein and protein-DNA complexes. They are generally composed
of a dozen components that are organized into ATP-powered protein complexes spanning the entire cell envelope. In this macromolecular secretion apparatus, the VirB1 component can lysis cell wall peptidoglycan of the bacteria to facilitate the assembly of T4SS . Many VirB1 components in gram-negative bacteria are lytic transglycosylases that can cleave the β-1,4 glycosidic bond between N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc), with the concomitant formation of a β-1,6-anhydromuramoyl product [24–27]. In some cases, the VirB1 orthologs can be N-acetylmuramoyl-L-alanine amidases that cleave the link between N-acetylmuramoyl residues and L-amino acid residues in certain cell wall glycopeptides . In this study, sequence alignment and phylogenetic analysis showed that the VirB1-89K protein may be an N-acetylmuramoyl-L-alanine amidase. To explore the potential role of VirB1-89K in S.