Peptidoglycan O-acetylesterase (Ape1), which is required for host survival in Neisseria sp., belongs to the diverse SGNH hydrolase superfamily, which includes important viral and bacterial virulence factors. Here, multi-domain crystal structures of Ape1 with an SGNH catalytic domain and a newly identified putative peptidoglycan-detection module are reported. Enzyme catalysis was performed in Ape1 crystals and key catalytic intermediates along the SGNH esterase hydrolysis reaction pathway were visualized, revealing a substrate-induced productive conformation of the catalytic triad, a mechanistic detail that has not previously been observed. This substrate-induced productive conformation of the catalytic triad shifts the established dogma on these enzymes, generating valuable insight into the structure-based design of drugs targeting the SGNH esterase superfamily.
Peptidoglycans (PGN) are a constituent of the bacterial cell wall, and are shed as bacteria divide. The presence of PGN is therefore a marker of bacterial activity that has been exploited by both plants and animals to induce defence mechanisms. Pattern recognition receptors that recognize PGN are extremely well conserved throughout evolution and shown to play important and diverse role in the development, homeostasis and activation of the immune system. In addition, PGN can be detected beyond mucosal surfaces, and their receptor can be expressed in tissues and cells that are far from the niches where bacteria reside. Thus, PGN affects not only the host's immunity, but also more generally the host's physiology. In this review, we discuss the biochemistry and biology of PGN, and their intriguing effects on the development of the immune system and the host physiology.
Abstract Ileal epithelial cell apoptosis and the local microbiota modulate the effects of oxaliplatin against proximal colon cancer by modulating tumor immunosurveillance. Here, we identified an ileal immune profile associated with the prognosis of colon cancer and responses to chemotherapy. The whole immune ileal transcriptome was upregulated in poor-prognosis patients with proximal colon cancer, while the colonic immunity of healthy and neoplastic areas was downregulated (except for the Th17 fingerprint) in such patients. Similar observations were made across experimental models of implanted and spontaneous murine colon cancer, showing a relationship between carcinogenesis and ileal inflammation. Conversely, oxaliplatin-based chemotherapy could restore a favorable, attenuated ileal immune fingerprint in responders. These results suggest that chemotherapy inversely shapes the immune profile of the ileum–tumor axis, influencing clinical outcome.
Germ-free (GF) mice have increased bone mass that is normalized by colonization with gut microbiota (GM) from conventionally raised (CONV-R) mice. To determine if innate immune signaling pathways mediated the effect of the GM, we studied the skeleton of GF and CONV-R mice with targeted inactivation of MYD88, NOD1 or NOD2. In contrast to WT and Myd88-/- mice, cortical bone thickness in mice lacking Nod1 or Nod2 was not increased under GF conditions. The expression of Tnfα and the osteoclastogenic factor Rankl in bone was reduced in GF compared to CONV-R WT mice but not in Nod1-/- or Nod2-/- mice indicating that the effect of the GM to increase Tnfα and Rankl in bone and to reduce bone mass is dependent on both NOD1 and NOD2 signaling.
Microbes and their byproducts have been reported to regulate host health and immune functions. Here we demonstrated that microbial exopolysaccharide produced by Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 (EPS-R1) induced CCR6+ CD8+ T cells of mice and humans. In mice, ingestion of EPS-R1 augmented antitumor effects of anti-CTLA-4 or anti-PD-1 monoclonal antibody against CCL20-expressing tumors, in which infiltrating CCR6+ CD8+ T cells were increased and produced IFNγ accompanied by a substantial immune response gene expression signature maintaining T-cell functions. Of note, the antitumor adjuvant effect of EPS-R1 was also observed in germ-free mice. Furthermore, the induction of CCR6 expression was mediated through the phosphorylated structure in EPS-R1 and a lysophosphatidic acid receptor on CD8+ T cells. Overall, we find that dietary EPS-R1 consumption induces CCR6+ CD8+ T cells in Peyer's patches, favoring a tumor microenvironment that augments the therapeutic effect of immune-checkpoint blockade depending on CCL20 production by tumors.Gut microbiota- and probiotic-derived metabolites are attractive agents to augment the efficacy of immunotherapies. Here we demonstrated that dietary consumption of Lactobacillus-derived exopolysaccharide induced CCR6+ CD8+ T cells in Peyer's patches and improved the tumor microenvironment to augment the therapeutic effects of immune-checkpoint blockade against CCL20-producing tumors. See related commentary by Di Luccia and Colonna, p. 1189. This article is highlighted in the In This Issue feature, p. 1171.
Peptidoglycan (PGN) and associated surface structures such as secondary polymers and capsules have a central role in the physiology of bacteria. The exoskeletal PGN heteropolymer is the major determinant of cell shape and allows bacteria to withstand cytoplasmic turgor pressure. Thus, its assembly, expansion, and remodeling during cell growth and division need to be highly regulated to avoid compromising cell survival. Similarly, regulation of the assembly impacts bacterial cell shape; distinct shapes enhance fitness in different ecological niches, such as the host. Because bacterial cell wall components, in particular PGN, are exposed to the environment and unique to bacteria, these have been coopted during evolution by eukaryotes to detect bacteria. Furthermore, the essential role of the cell wall in bacterial survival has made PGN an important signaling molecule in the dialog between host and microbes and a target of many host responses. Millions of years of coevolution have resulted in a pivotal role for PGN fragments in shaping host physiology and in establishing a long-lasting symbiosis between microbes and the host. Thus, perturbations of this dialog can lead to pathologies such as chronic inflammatory diseases. Similarly, pathogens have devised sophisticated strategies to manipulate the system to enhance their survival and growth.
In Figure 4 and Figure S9, the panels were initially built as a single field with pasted representative images of each strain. However, the use of such composite images is against the journal policy, and we apologize for this mistake. The two figures were remade according to the journal's policy and each panel is now composed of the same images presented individually. These corrections do not affect our conclusions on the differential localisation of GFP-hpMotB between wild type E. coli and their corresponding lytic transglycosylase mutants, as these individual images were part of the 100 fluorescent bacteria of each strain that were used to obtained the data presented in the two bar graphs of Figure 4 and Figure S9. Fig. 4. Localization of hpMotB in E. coli strains. Fluorescence microscopy of the different E. coli strains harboring plasmid pAM001. In wild type strains MC1061 pAM001 and MG1655 pAM001, GFP-hpMotB was clearly localized at the bacterial pole, whereas in the LTG mutant strains, MHD79 pAM001 and MG1655 sltΩKm pAM001, the fluorescent protein was distributed over the entire bacterial surface. Each panel presents representative images of each strain. The graph represents the percentage of bacteria possessing polar patches with respect to the total fluorescent bacteria. For each strain, 100 fluorescent bacteria were observed. Fig. S9. Fluorescence microscopy of the different E. coli strains harboring plasmid pMAB002. The IcsA507-620-GFPmut2 fusion protein was clearly localized at the bacterial pole of wild type strains MC1061 pMAB002 and MG1655 pMAB002, as well as in the LTG mutant strains MHD79 pMAB002 and MG1566 sltΩKm pMAB002. Each panel presents representative images of each strain. The graph represents the percentage of bacteria possessing polar patches with respect to the total numbers of fluorescent bacteria. For each strain, 100 fluorescent bacteria were observed.
