-
Nature Sep 2022Bacterial cell wall components provide various unique molecular structures that are detected by pattern recognition receptors (PRRs) of the innate immune system as...
Bacterial cell wall components provide various unique molecular structures that are detected by pattern recognition receptors (PRRs) of the innate immune system as non-self. Most bacterial species form a cell wall that consists of peptidoglycan (PGN), a polymeric structure comprising alternating amino sugars that form strands cross-linked by short peptides. Muramyl dipeptide (MDP) has been well documented as a minimal immunogenic component of peptidoglycan. MDP is sensed by the cytosolic nucleotide-binding oligomerization domain-containing protein 2 (NOD2). Upon engagement, it triggers pro-inflammatory gene expression, and this functionality is of critical importance in maintaining a healthy intestinal barrier function. Here, using a forward genetic screen to identify factors required for MDP detection, we identified N-acetylglucosamine kinase (NAGK) as being essential for the immunostimulatory activity of MDP. NAGK is broadly expressed in immune cells and has previously been described to contribute to the hexosamine biosynthetic salvage pathway. Mechanistically, NAGK functions upstream of NOD2 by directly phosphorylating the N-acetylmuramic acid moiety of MDP at the hydroxyl group of its C6 position, yielding 6-O-phospho-MDP. NAGK-phosphorylated MDP-but not unmodified MDP-constitutes an agonist for NOD2. Macrophages from mice deficient in NAGK are completely deficient in MDP sensing. These results reveal a link between amino sugar metabolism and innate immunity to bacterial cell walls.
Topics: Acetylmuramyl-Alanyl-Isoglutamine; Animals; Bacteria; Cell Wall; Hexosamines; Immunity, Innate; Macrophages; Mice; Nod2 Signaling Adaptor Protein; Peptidoglycan; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor)
PubMed: 36002575
DOI: 10.1038/s41586-022-05125-x -
The FEBS Journal Aug 2022The peptidoglycan (PG) cell wall is an essential polymer for the shape and viability of bacteria. Its protective role is in great part provided by its mesh-like... (Review)
Review
The peptidoglycan (PG) cell wall is an essential polymer for the shape and viability of bacteria. Its protective role is in great part provided by its mesh-like character. Therefore, PG-cross-linking enzymes like the penicillin-binding proteins (PBPs) are among the best targets for antibiotics. However, while PBPs have been in the spotlight for more than 50 years, another class of PG-cross-linking enzymes called LD-transpeptidases (LDTs) seemed to contribute less to PG synthesis and, thus, has kept an aura of mystery. In the last years, a number of studies have associated LDTs with cell wall adaptation to stress including β-lactam antibiotics, outer membrane stability, and toxin delivery, which has shed light onto the biological meaning of these proteins. Furthermore, as some species display a great abundance of LD-cross-links in their cell wall, it has been hypothesized that LDTs could also be the main synthetic PG-transpeptidases in some bacteria. In this review, we introduce these enzymes and their role in PG biosynthesis and we highlight the most recent advances in understanding their biological role in diverse species.
Topics: Anti-Bacterial Agents; Bacterial Proteins; Cell Wall; Penicillin-Binding Proteins; Peptidoglycan; Peptidyl Transferases
PubMed: 34109739
DOI: 10.1111/febs.16066 -
International Journal of Molecular... Mar 2022The synthesis of a peptidoglycan septum is a fundamental part of bacterial fission and is driven by a multiprotein dynamic complex called the divisome. FtsW and FtsI are... (Review)
Review
The synthesis of a peptidoglycan septum is a fundamental part of bacterial fission and is driven by a multiprotein dynamic complex called the divisome. FtsW and FtsI are essential proteins that synthesize the peptidoglycan septum and are controlled by the regulatory FtsBLQ subcomplex and the activator FtsN. However, their mode of regulation has not yet been uncovered in detail. Understanding this process in detail may enable the development of new compounds to combat the rise in antibiotic resistance. In this review, recent data on the regulation of septal peptidoglycan synthesis is summarized and discussed. Based on structural models and the collected data, multiple putative interactions within FtsWI and with regulators are uncovered. This elaborates on and supports an earlier proposed model that describes active and inactive conformations of the septal peptidoglycan synthesis complex that are stabilized by these interactions. Furthermore, a new model on the spatial organization of the newly synthesized peptidoglycan and the synthesis complex is presented. Overall, the updated model proposes a balance between several allosteric interactions that determine the state of septal peptidoglycan synthesis.
Topics: Bacterial Proteins; Cell Wall; Membrane Proteins; Peptidoglycan
PubMed: 35408901
DOI: 10.3390/ijms23073537 -
Current Opinion in Cell Biology Feb 2021Bacterial cell division is orchestrated by the divisome, a protein complex centered on the tubulin homolog FtsZ. FtsZ polymerizes into a dynamic ring that defines the... (Review)
Review
Bacterial cell division is orchestrated by the divisome, a protein complex centered on the tubulin homolog FtsZ. FtsZ polymerizes into a dynamic ring that defines the division site, recruits downstream proteins, and directs peptidoglycan synthesis to drive constriction. Recent studies have documented treadmilling of FtsZ polymer clusters both in cells and in vitro. Emerging evidence suggests that FtsZ dynamics are regulated largely by intrinsic properties of FtsZ itself and by the membrane anchoring protein FtsA. Although FtsZ dynamics are broadly required for Z-ring assembly, their role(s) during constriction may vary among bacterial species. These recent advances set the stage for future studies to investigate how FtsZ dynamics are physically and/or functionally coupled to peptidoglycan metabolic enzymes to direct efficient division.
Topics: Bacteria; Bacterial Proteins; Cell Division; Cell Wall; Cytoskeletal Proteins; Peptidoglycan
PubMed: 33220539
DOI: 10.1016/j.ceb.2020.10.013 -
Proceedings of the National Academy of... Jun 2023AmiA and AmiB are peptidoglycan-hydrolyzing enzymes from that are required to break the peptidoglycan layer during bacterial cell division and maintain integrity of...
AmiA and AmiB are peptidoglycan-hydrolyzing enzymes from that are required to break the peptidoglycan layer during bacterial cell division and maintain integrity of the cell envelope. In vivo, the activity of AmiA and AmiB is tightly controlled through their interactions with the membrane-bound FtsEX-EnvC complex. Activation of AmiA and AmiB requires access to a groove in the amidase-activating LytM domain of EnvC which is gated by ATP-driven conformational changes in FtsEX-EnvC complex. Here, we present a high-resolution structure of the isolated AmiA protein, confirming that it is autoinhibited in the same manner as AmiB and AmiC, and a complex of the AmiB enzymatic domain bound to the activating EnvC LytM domain. In isolation, the active site of AmiA is blocked by an autoinhibitory helix that binds directly to the catalytic zinc and fills the volume expected to accommodate peptidoglycan binding. In the complex, binding of the EnvC LytM domain induces a conformational change that displaces the amidase autoinhibitory helix and reorganizes the active site for activity. Our structures, together with complementary mutagenesis work, defines the conformational changes required to activate AmiA and/or AmiB through their interaction with their cognate activator EnvC.
Topics: Escherichia coli Proteins; Peptidoglycan; N-Acetylmuramoyl-L-alanine Amidase; Escherichia coli; Amidohydrolases; Bacterial Proteins
PubMed: 37276423
DOI: 10.1073/pnas.2302580120 -
Nature Reviews. Microbiology Jul 2019The Gram-negative envelope is a complex structure that consists of the inner membrane, the periplasm, peptidoglycan and the outer membrane, and protects the bacterial... (Review)
Review
The Gram-negative envelope is a complex structure that consists of the inner membrane, the periplasm, peptidoglycan and the outer membrane, and protects the bacterial cell from the environment. Changing environmental conditions can cause damage, which triggers the envelope stress responses to maintain cellular homeostasis. In this Review, we explore the causes, both environmental and intrinsic, of envelope stress, as well as the cellular stress response pathways that counter these stresses. Furthermore, we discuss the damage to the cell that occurs when these pathways are aberrantly activated either in the absence of stress or to an excessive degree. Finally, we review the mechanisms whereby the σ response constantly acts to prevent cell death caused by highly toxic unfolded outer membrane proteins. Together, the recent work that we discuss has provided insights that emphasize the necessity for proper levels of stress response activation and the detrimental consequences that can occur in the absence of proper regulation.
Topics: Bacterial Outer Membrane; Bacterial Proteins; Cell Membrane; Cell Wall; Gene Expression Regulation, Bacterial; Gram-Negative Bacteria; Lipopolysaccharides; Microbial Viability; Peptidoglycan; Sigma Factor; Stress, Physiological
PubMed: 31150012
DOI: 10.1038/s41579-019-0199-0 -
The ISME Journal Jul 2023Although the phylum Chloroflexota is ubiquitous, its biology and evolution are poorly understood due to limited cultivability. Here, we isolated two motile, thermophilic...
Although the phylum Chloroflexota is ubiquitous, its biology and evolution are poorly understood due to limited cultivability. Here, we isolated two motile, thermophilic bacteria from hot spring sediments belonging to the genus Tepidiforma and class Dehalococcoidia within the phylum Chloroflexota. A combination of cryo-electron tomography, exometabolomics, and cultivation experiments using stable isotopes of carbon revealed three unusual traits: flagellar motility, a peptidoglycan-containing cell envelope, and heterotrophic activity on aromatics and plant-associated compounds. Outside of this genus, flagellar motility has not been observed in Chloroflexota, and peptidoglycan-containing cell envelopes have not been described in Dehalococcoidia. Although these traits are unusual among cultivated Chloroflexota and Dehalococcoidia, ancestral character state reconstructions showed flagellar motility and peptidoglycan-containing cell envelopes were ancestral within the Dehalococcoidia, and subsequently lost prior to a major adaptive radiation of Dehalococcoidia into marine environments. However, despite the predominantly vertical evolutionary histories of flagellar motility and peptidoglycan biosynthesis, the evolution of enzymes for degradation of aromatics and plant-associated compounds was predominantly horizontal and complex. Together, the presence of these unusual traits in Dehalococcoidia and their evolutionary histories raise new questions about the timing and selective forces driving their successful niche expansion into global oceans.
Topics: Phylogeny; Peptidoglycan; Bacteria; Chloroflexi; Phenotype
PubMed: 37041326
DOI: 10.1038/s41396-023-01405-0 -
ACS Infectious Diseases Jul 2020This review highlights recent efforts to detect bacteria using engineered small molecules that are processed and incorporated similarly to their natural counterparts.... (Review)
Review
This review highlights recent efforts to detect bacteria using engineered small molecules that are processed and incorporated similarly to their natural counterparts. There are both scientific and clinical justifications for these endeavors. The use of detectable, cell-wall targeted chemical probes has elucidated microbial behavior, with several fluorescent labeling methods in widespread laboratory use. Furthermore, many existing efforts including ours, focus on developing new imaging tools to study infection in clinical practice. The bacterial cell wall, a remarkably rich and complex structure, is an outstanding target for bacteria-specific detection. Several cell wall components are found in bacteria but not mammals, especially peptidoglycan, lipopolysaccharide, and teichoic acids. As this review highlights, the development of laboratory tools for fluorescence microscopy has vastly outstripped related positron emission tomography (PET) or single photon emission computed tomography (SPECT) radiotracer development. However, there is great synergy between these chemical strategies, which both employ mimicry of endogenous substrates to incorporate detectable structures. As the field of bacteria-specific imaging grows, it will be important to understand the mechanisms involved in microbial incorporation of radionuclides. Additionally, we will highlight the clinical challenges motivating this imaging effort.
Topics: Bacteria; Cell Wall; Peptidoglycan; Positron-Emission Tomography; Teichoic Acids
PubMed: 32433879
DOI: 10.1021/acsinfecdis.9b00515 -
Molecular Microbiology Mar 2020Teichoic acids (TAs) are the most abundant glycopolymers in the cell wall of Listeria, an opportunistic Gram-positive pathogen that causes severe foodborne infections.... (Review)
Review
Teichoic acids (TAs) are the most abundant glycopolymers in the cell wall of Listeria, an opportunistic Gram-positive pathogen that causes severe foodborne infections. Two different structural classes of Listeria TA exist: the polyribitolphosphate-based wall teichoic acid (WTA) that is covalently anchored to the peptidoglycan, and the polyglycerolphosphate-based lipoteichoic acid (LTA) that is tethered to the cytoplasmic membrane. While TA polymers govern many important physiological processes, the diverse glycosylation patterns of WTA result in a high degree of surface variation across the species and serovars of Listeria, which in turn bestows varying effects on fitness, biofilm formation, bacteriophage susceptibility and virulence. We review the advances made over the past two decades, and our current understanding of the relationship between TA structure and function. We describe the various types of TA that have been structurally determined to date, and discuss the genetic determinants known to be involved in TA glycosylation. We elaborate on surface proteins functionally related to TA decoration, as well as the molecular and analytical tools used to probe TAs. We anticipate that the growing knowledge of the Listeria surface chemistry will also be exploited to develop novel diagnostic and therapeutic strategies for this pathogen.
Topics: Cell Membrane; Cell Wall; Glycosylation; Lipopolysaccharides; Listeria; Membrane Proteins; Peptidoglycan; Structure-Activity Relationship; Teichoic Acids; Virulence
PubMed: 31972870
DOI: 10.1111/mmi.14472 -
Proceedings of the National Academy of... Jun 2023The Gram-negative bacterial cell envelope is a complex multilayered structure comprising a bilayered phospholipid (PL) membrane that surrounds the cytoplasm (inner...
The Gram-negative bacterial cell envelope is a complex multilayered structure comprising a bilayered phospholipid (PL) membrane that surrounds the cytoplasm (inner membrane or IM) and an asymmetric outer membrane (OM) with PLs in the inner leaflet and lipopolysaccharides in the outer leaflet. Between these two layers is the periplasmic space, which contains a highly cross-linked mesh-like glycan polymer, peptidoglycan (PG). During cell expansion, coordinated synthesis of each of these components is required to maintain the integrity of the cell envelope; however, it is currently not clear how such coordination is achieved. In this study, we show that a cross-link-specific PG hydrolase couples the expansion of PG sacculus with that of PL synthesis in the Gram-negative model bacterium, . We find that unregulated activity of a PG hydrolytic enzyme, MepS is detrimental for growth of during fatty acid (FA)-limiting conditions. Further genetic and biochemical analyses revealed that cellular availability of FA or PL alters the post-translational stability of MepS by modulating the proteolytic activity of a periplasmic adaptor-protease complex, NlpI-Prc toward MepS. Our results indicate that loss of OM lipid asymmetry caused by alterations in PL abundance leads to the generation of a signal to the NlpI-Prc complex for the stabilization of MepS, which subsequently cleaves the cross-links to facilitate expansion of PG. In summary, our study shows the existence of a molecular cross-talk that enables coordinated expansion of the PG sacculus with that of membrane synthesis for balanced cell-envelope biogenesis.
Topics: Escherichia coli; Escherichia coli Proteins; Peptidoglycan; Hydrolases; Cell Wall; Gram-Negative Bacteria; Phospholipids; Lipoproteins; Cysteine Endopeptidases
PubMed: 37276399
DOI: 10.1073/pnas.2300784120