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EcoSal Plus Jan 2021Peptidoglycan is a defining feature of the bacterial cell wall. Initially identified as a target of the revolutionary beta-lactam antibiotics, peptidoglycan has become a...
Peptidoglycan is a defining feature of the bacterial cell wall. Initially identified as a target of the revolutionary beta-lactam antibiotics, peptidoglycan has become a subject of much interest for its biology, its potential for the discovery of novel antibiotic targets, and its role in infection. Peptidoglycan is a large polymer that forms a mesh-like scaffold around the bacterial cytoplasmic membrane. Peptidoglycan synthesis is vital at several stages of the bacterial cell cycle: for expansion of the scaffold during cell elongation and for formation of a septum during cell division. It is a complex multifactorial process that includes formation of monomeric precursors in the cytoplasm, their transport to the periplasm, and polymerization to form a functional peptidoglycan sacculus. These processes require spatio-temporal regulation for successful assembly of a robust sacculus to protect the cell from turgor and determine cell shape. A century of research has uncovered the fundamentals of peptidoglycan biology, and recent studies employing advanced technologies have shed new light on the molecular interactions that govern peptidoglycan synthesis. Here, we describe the peptidoglycan structure, synthesis, and regulation in rod-shaped bacteria, particularly , with a few examples from and other diverse organisms. We focus on the pathway of peptidoglycan sacculus elongation, with special emphasis on discoveries of the past decade that have shaped our understanding of peptidoglycan biology.
Topics: Cell Division; Cell Membrane; Cell Wall; Escherichia coli; Peptidoglycan
PubMed: 33470191
DOI: 10.1128/ecosalplus.ESP-0010-2020 -
Immunological Reviews Sep 2020It has been long recognized that NOD1 and NOD2 are critical players in the host immune response, primarily by their sensing bacterial peptidoglycan-conserved motifs.... (Review)
Review
It has been long recognized that NOD1 and NOD2 are critical players in the host immune response, primarily by their sensing bacterial peptidoglycan-conserved motifs. Significant advances have been made from efforts that characterize their upstream activators, assembly of signaling complexes, and activation of downstream signaling pathways. Disruption in NOD1 and NOD2 signaling has also been associated with impaired host defense and resistance to the development of inflammatory diseases. In this review, we will describe how NOD1 and NOD2 sense microbes and cellular stress to regulate host responses that can affect disease pathogenesis and outcomes.
Topics: Communicable Diseases; Humans; Immunity, Innate; Nod1 Signaling Adaptor Protein; Nod2 Signaling Adaptor Protein; Peptidoglycan
PubMed: 32677123
DOI: 10.1111/imr.12902 -
Viruses Apr 2021Antibiotic-resistant pathogens are increasingly more prevalent and problematic. Traditional antibiotics are no longer a viable option for dealing with these... (Review)
Review
Antibiotic-resistant pathogens are increasingly more prevalent and problematic. Traditional antibiotics are no longer a viable option for dealing with these multidrug-resistant microbes and so new approaches are needed. Bacteriophage-derived proteins such as endolysins could offer one effective solution. Endolysins are bacteriophage-encoded peptidoglycan hydrolases that act to lyse bacterial cells by targeting their cell's wall, particularly in Gram-positive bacteria due to their naturally exposed peptidoglycan layer. These lytic enzymes have received much interest from the scientific community in recent years for their specificity, mode of action, potential for engineering, and lack of resistance mechanisms. Over the past decade, a renewed interest in endolysin therapy has led to a number of successful applications. Recombinant endolysins have been shown to be effective against prominent pathogens such as MRSA, strains in biofilm formation, and . Endolysins have also been studied in combination with other antimicrobials, giving a synergistic effect. Although endolysin therapy comes with some regulatory and logistical hurdles, the future looks promising, with the emergence of engineered "next-generation" lysins. This review will focus on the likelihood that endolysins will become a viable new antimicrobial therapy and the challenges that may have to be overcome along the way.
Topics: Animals; Bacteriophages; Cell Wall; Endopeptidases; Gram-Positive Bacterial Infections; Humans; Peptidoglycan; Phage Therapy
PubMed: 33920965
DOI: 10.3390/v13040680 -
Science (New York, N.Y.) Apr 2022Gut bacteria influence brain functions and metabolism. We investigated whether this influence can be mediated by direct sensing of bacterial cell wall components by...
Gut bacteria influence brain functions and metabolism. We investigated whether this influence can be mediated by direct sensing of bacterial cell wall components by brain neurons. In mice, we found that bacterial peptidoglycan plays a major role in mediating gut-brain communication via the Nod2 receptor. Peptidoglycan-derived muropeptides reach the brain and alter the activity of a subset of brain neurons that express Nod2. Activation of Nod2 in hypothalamic inhibitory neurons is essential for proper appetite and body temperature control, primarily in females. This study identifies a microbe-sensing mechanism that regulates feeding behavior and host metabolism.
Topics: Animals; Appetite; Bacteria; Body Temperature; Mice; Neurons; Nod2 Signaling Adaptor Protein; Peptidoglycan
PubMed: 35420957
DOI: 10.1126/science.abj3986 -
Cell Host & Microbe Oct 2022The pattern-recognition receptor NOD2 senses bacterial muropeptides to regulate host immunity and maintain homeostasis. Loss-of-function mutations in NOD2 are associated...
The pattern-recognition receptor NOD2 senses bacterial muropeptides to regulate host immunity and maintain homeostasis. Loss-of-function mutations in NOD2 are associated with Crohn's disease (CD), but how the variations in microbial factors influence NOD2 signaling and host pathology is elusive. We demonstrate that the Firmicutes peptidoglycan remodeling enzyme, DL-endopeptidase, increased the NOD2 ligand level in the gut and impacted colitis outcomes. Metagenomic analyses of global cohorts (n = 857) revealed that DL-endopeptidase gene abundance decreased globally in CD patients and negatively correlated with colitis. Fecal microbiota from CD patients with low DL-endopeptidase activity predisposed mice to colitis. Administering DL-endopeptidase, but not an active site mutant, alleviated colitis via the NOD2 pathway. Therapeutically restoring NOD2 ligands with a DL-endopeptidase-producing Lactobacillus salivarius strain or mifamurtide, a clinical analog of muramyl dipeptide, exerted potent anti-colitis effects. Our study suggests that the depletion of DL-endopeptidase contributes to CD pathogenesis through NOD2 signaling, providing a therapeutically modifiable target.
Topics: Acetylmuramyl-Alanyl-Isoglutamine; Animals; Colitis; Crohn Disease; Endopeptidases; Gastrointestinal Microbiome; Ligands; Mice; Nod2 Signaling Adaptor Protein; Peptidoglycan
PubMed: 36049483
DOI: 10.1016/j.chom.2022.08.002 -
Immunity May 2023Cytosolic innate immune sensing is critical for protecting barrier tissues. NOD1 and NOD2 are cytosolic sensors of small peptidoglycan fragments (muropeptides) derived...
Cytosolic innate immune sensing is critical for protecting barrier tissues. NOD1 and NOD2 are cytosolic sensors of small peptidoglycan fragments (muropeptides) derived from the bacterial cell wall. These muropeptides enter cells, especially epithelial cells, through unclear mechanisms. We previously implicated SLC46 transporters in muropeptide transport in Drosophila immunity. Here, we focused on Slc46a2, which was highly expressed in mammalian epidermal keratinocytes, and showed that it was critical for the delivery of diaminopimelic acid (DAP)-muropeptides and activation of NOD1 in keratinocytes, whereas the related transporter Slc46a3 was critical for delivering the NOD2 ligand MDP to keratinocytes. In a mouse model, Slc46a2 and Nod1 deficiency strongly suppressed psoriatic inflammation, whereas methotrexate, a commonly used psoriasis therapeutic, inhibited Slc46a2-dependent transport of DAP-muropeptides. Collectively, these studies define SLC46A2 as a transporter of NOD1-activating muropeptides, with critical roles in the skin barrier, and identify this transporter as an important target for anti-inflammatory intervention.
Topics: Mice; Animals; Methotrexate; Inflammation; Peptidoglycan; Epithelial Cells; Dermatitis; Nod1 Signaling Adaptor Protein; Nod2 Signaling Adaptor Protein; Immunity, Innate; Mammals
PubMed: 37116499
DOI: 10.1016/j.immuni.2023.04.001 -
Nature Mar 2023Gram-negative bacteria surround their cytoplasmic membrane with a peptidoglycan (PG) cell wall and an outer membrane (OM) with an outer leaflet composed of...
Gram-negative bacteria surround their cytoplasmic membrane with a peptidoglycan (PG) cell wall and an outer membrane (OM) with an outer leaflet composed of lipopolysaccharide (LPS). This complex envelope presents a formidable barrier to drug entry and is a major determinant of the intrinsic antibiotic resistance of these organisms. The biogenesis pathways that build the surface are also targets of many of our most effective antibacterial therapies. Understanding the molecular mechanisms underlying the assembly of the Gram-negative envelope therefore promises to aid the development of new treatments effective against the growing problem of drug-resistant infections. Although the individual pathways for PG and OM synthesis and assembly are well characterized, almost nothing is known about how the biogenesis of these essential surface layers is coordinated. Here we report the discovery of a regulatory interaction between the committed enzymes for the PG and LPS synthesis pathways in the Gram-negative pathogen Pseudomonas aeruginosa. We show that the PG synthesis enzyme MurA interacts directly and specifically with the LPS synthesis enzyme LpxC. Moreover, MurA was shown to stimulate LpxC activity in cells and in a purified system. Our results support a model in which the assembly of the PG and OM layers in many proteobacterial species is coordinated by linking the activities of the committed enzymes in their respective synthesis pathways.
Topics: Cell Wall; Lipopolysaccharides; Bacterial Outer Membrane; Pseudomonas aeruginosa; Peptidoglycan
PubMed: 36859542
DOI: 10.1038/s41586-023-05750-0 -
Microbiology Spectrum Jul 2019The highly cross-linked peptidoglycan represents the rigid layer of the bacterial envelope and protects bacteria from osmotic lysis. In Gram-positive bacteria,... (Review)
Review
The highly cross-linked peptidoglycan represents the rigid layer of the bacterial envelope and protects bacteria from osmotic lysis. In Gram-positive bacteria, peptidoglycan also functions as a scaffold for the immobilization of capsular polysaccharide, wall teichoic acid (WTA), and surface proteins. This chapter captures recent development on the assembly of the envelope of including mechanisms accounting for immobilization of molecules to peptidoglycan as well as hydrolysis of peptidoglycan for the specific release of bound molecules, facilitation of protein secretion across the envelope and cell division. Peptidoglycan, WTA and capsular polysaccharide are directly synthesized onto undecaprenol. Surface proteins are anchored by Sortase A, a membrane-embedded transpeptidase that scans secreted polypeptides for the C-terminal LPXTG motif of sorting signals. The resulting acyl enzyme intermediate is resolved by lipid II, the undecaprenol-bound peptidoglycan precursor. While these pathways share membrane diffusible undecaprenol, assembly of these molecules occurs either at the cross-walls or the cell poles. In , the cross-wall represents the site of peptidoglycan synthesis which is eventually split to complete the cell cycle yielding newly divided daughter cells. Peptidoglycan synthesized at the cross-wall is initially devoid of WTA. Conversely, lipoteichoic acid (LTA) synthesis which does not require bactoprenol is seemingly restricted to septal membranes. Similarly, distinguishes two types of surface protein precursors. Polypeptides with canonical signal peptides are deposited at the cell poles, whereas precursors with conserved YSIRK-GXXS motif signal peptides traffic to the cross-wall. A model for protein trafficking in the envelope and uneven distribution of teichoic acids is discussed.
Topics: Animals; Bacterial Proteins; Cell Membrane; Cell Wall; Humans; Membrane Proteins; Peptidoglycan; Protein Transport; Staphylococcal Infections; Staphylococcus aureus
PubMed: 31267890
DOI: 10.1128/microbiolspec.GPP3-0070-2019 -
Nature Jun 2022Linkages between the outer membrane of Gram-negative bacteria and the peptidoglycan layer are crucial for the maintenance of cellular integrity and enable survival in...
Linkages between the outer membrane of Gram-negative bacteria and the peptidoglycan layer are crucial for the maintenance of cellular integrity and enable survival in challenging environments. The function of the outer membrane is dependent on outer membrane proteins (OMPs), which are inserted into the membrane by the β-barrel assembly machine (BAM). Growing Escherichia coli cells segregate old OMPs towards the poles by a process known as binary partitioning, the basis of which is unknown. Here we demonstrate that peptidoglycan underpins the spatiotemporal organization of OMPs. Mature, tetrapeptide-rich peptidoglycan binds to BAM components and suppresses OMP foldase activity. Nascent peptidoglycan, which is enriched in pentapeptides and concentrated at septa, associates with BAM poorly and has little effect on its activity, leading to preferential insertion of OMPs at division sites. The synchronization of OMP biogenesis with cell wall growth results in the binary partitioning of OMPs as cells divide. Our study reveals that Gram-negative bacteria coordinate the assembly of two major cell envelope layers by rendering OMP biogenesis responsive to peptidoglycan maturation, a potential vulnerability that could be exploited in future antibiotic design.
Topics: Bacterial Outer Membrane Proteins; Cell Membrane; Cell Wall; Escherichia coli; Escherichia coli Proteins; Peptidoglycan; Protein Folding
PubMed: 35705811
DOI: 10.1038/s41586-022-04834-7 -
Nature Communications Jun 2023Secreted proteins are one of the direct molecular mechanisms by which microbiota influence the host, thus constituting a promising field for drug discovery. Here,...
Secreted proteins are one of the direct molecular mechanisms by which microbiota influence the host, thus constituting a promising field for drug discovery. Here, through bioinformatics-guided screening of the secretome of clinically established probiotics from Lactobacillus, we identify an uncharacterized secreted protein (named LPH here) that is shared by most of these probiotic strains (8/10) and demonstrate that it protects female mice from colitis in multiple models. Functional studies show that LPH is a bi-functional peptidoglycan hydrolase with both N-Acetyl-β-D-muramidase and DL-endopeptidase activities that can generate muramyl dipeptide (MDP), a NOD2 ligand. Different active site mutants of LPH in combination with Nod2 knockout female mice confirm that LPH exerts anti-colitis effects through MDP-NOD2 signaling. Furthermore, we validate that LPH can also exert protective effects on inflammation-associated colorectal cancer in female mice. Our study reports a probiotic enzyme that enhances NOD2 signaling in vivo in female mice and describes a molecular mechanism that may contribute to the effects of traditional Lactobacillus probiotics.
Topics: Mice; Female; Animals; Ligands; N-Acetylmuramoyl-L-alanine Amidase; Acetylmuramyl-Alanyl-Isoglutamine; Colitis; Mice, Knockout; Probiotics; Nod2 Signaling Adaptor Protein; Peptidoglycan
PubMed: 37286542
DOI: 10.1038/s41467-023-38950-3