The normal, unmodified glycan strands of bacterial peptidoglycan consist of alternating residues of β-1,4-linked N-acetylmuramic acid and N-acetylglucosamine. In many species the glycan strands ...become modified after their insertion into the cell wall. This review describes the structure of secondary modifications and of attachment sites of surface polymers in the glycan strands of peptidoglycan. It also provides an overview of the occurrence of these modifications in various bacterial species. Recently, enzymes responsible for the N-deacetylation, N-glycolylation and O-acetylation of the glycan strands were identified. The presence of these modifications affects the hydrolysis of peptidoglycan and its enlargement during cell growth. Glycan strands are frequently deacetylated and/or O-acetylated in pathogenic species. These alterations affect the recognition of bacteria by host factors, and contribute to the resistance of bacteria to host defence factors such as lysozyme.
Summary
Most bacteria surround their cytoplasmic membrane with a net‐like, elastic heteropolymer, the peptidoglycan sacculus, to protect themselves from bursting due to the turgor and to maintain ...cell shape. It has been assumed that growing bacteria require peptidoglycan hydrolases to open meshes in the peptidoglycan net allowing the insertion of the newly synthesized material for surface expansion. However, peptidoglycan hydrolases essential for bacterial growth have long remained elusive. In this issue of Molecular Microbiology Singh et al. () report the identification in Escherichia coli of three new DD‐endopeptidases (Spr, YdhO and YebA) which are collectively required for peptidoglycan growth. Cells depleted of the three enzymes fail to incorporate new peptidoglycan, indicating that the cleavage of cross‐links by the new endopeptidases is needed for surface growth of the sacculus. These results are corroborated by recent data showing that Bacillus subtilis cells require the DL‐endopeptidase activity of CwlO or LytE for growth.
Bacteria surround their cell membrane with a net-like peptidoglycan layer, called sacculus, to protect the cell from bursting and maintain its cell shape. Sacculus growth during elongation and cell ...division is mediated by dynamic and transient multiprotein complexes, the elongasome and divisome, respectively. In this Review we present our current understanding of how peptidoglycan synthases are regulated by multiple and specific interactions with cell morphogenesis proteins that are linked to a dynamic cytoskeletal protein, either the actin-like MreB or the tubulin-like FtsZ. Several peptidoglycan synthases and hydrolases require activation by outer-membrane-anchored lipoproteins. We also discuss how bacteria achieve robust cell wall growth under different conditions and stresses by maintaining multiple peptidoglycan enzymes and regulators as well as different peptidoglycan growth mechanisms, and we present the emerging role of LD-transpeptidases in peptidoglycan remodelling.
In the recent decade, our view on the organization of the bacterial cell has been revolutionized by the identification of cytoskeletal elements. Most bacterial species have structural homologs of ...actin and tubulin that assemble into dynamic, filamentous structures at precisely defined sub-cellular locations. The essential cell division protein FtsZ forms a dynamic ring at mid-cell and is similar in its structure to tubulin. Proteins of the MreB family, which are structural homologs of actin, assemble into helical or straight filaments in the bacterial cytoplasm. As in eukaryotic cells, the bacterial cytoskeleton drives essential cellular processes such as cell division, cell wall growth, DNA movement, protein targeting, and alignment of organelles. Different high-throughput assays have been developed to search for inhibitors of components of the bacterial cytoskeleton. Cell-based assays for the detection of cell division inhibitors as well as FtsZ GTPase assays led to the identification of several compounds that inhibit the polymerization of FtsZ, by this blocking bacterial cell division. Such inhibitors might not only be valuable tools for basic research, but might also lead to novel therapeutic agents against pathogenic bacteria. For example, the polyphenol dichamanetin, the 2-alkoxycarbonylaminopyridine SRI-3072, and the benzophenanthridine alkaloid sanguinarine inhibit the GTPase activity of FtsZ and exhibit antimicrobial activity.
The periplasmic murein (peptidoglycan) sacculus is a giant macromolecule made of glycan strands cross-linked by short peptides completely surrounding the cytoplasmic membrane to protect the cell from ...lysis due to its internal osmotic pressure. More than 50 different muropeptides are released from the sacculus by treatment with a muramidase.
Escherichia coli has six murein synthases which enlarge the sacculus by transglycosylation and transpeptidation of lipid II precursor. A set of twelve periplasmic murein hydrolases (autolysins) release murein fragments during cell growth and division. Recent data on the in vitro murein synthesis activities of the murein synthases and on the interactions between murein synthases, hydrolases and cell cycle related proteins are being summarized. There are different models for the architecture of murein and for the incorporation of new precursor into the sacculus. We present a model in which morphogenesis of the rod-shaped
E. coli is driven by cytoskeleton elements competing for the control over the murein synthesis multi-enzyme complexes.
How bacteria grow and divide while retaining a defined shape is a fundamental question in microbiology, but technological advances are now driving a new understanding of how the shape-maintaining ...bacterial peptidoglycan sacculus grows. In this Review, we highlight the relationship between peptidoglycan synthesis complexes and cytoskeletal elements, as well as recent evidence that peptidoglycan growth is regulated from outside the sacculus in Gram-negative bacteria. We also discuss how growth of the sacculus is sensitive to mechanical force and nutritional status, and describe the roles of peptidoglycan hydrolases in generating cell shape and of D-amino acids in sacculus remodelling.
Peptidoglycan forms a net-like sacculus made of glycan strands crosslinked by peptides. The length of the glycan strands and the degree of crosslinkage vary with bacterial species, strains and growth ...conditions. Several models for the three-dimensional architecture of peptidoglycan have been proposed, some of which have been tested experimentally. The new data support a layered model in Gram-negative bacteria, and a more elaborate peptidoglycan architecture, with bands made of coiled bundles of glycan strands, in the rod-shaped Bacillus subtilis . However, many questions remain unanswered and, therefore, more data and more models are required to decipher the complex cell wall architecture in bacteria.
The physiology of bacterial cell division Egan, Alexander J. F.; Vollmer, Waldemar
Annals of the New York Academy of Sciences,
January 2013, Letnik:
1277, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Bacterial cell division is facilitated by the divisome, a dynamic multiprotein assembly localizing at mid‐cell to synthesize the stress‐bearing peptidoglycan and to constrict all cell envelope ...layers. Divisome assembly occurs in two steps and involves multiple interactions between more than 20 essential and accessory cell division proteins. Well before constriction and while the cell is still elongating, the tubulin‐like FtsZ and early cell division proteins form a ring‐like structure at mid‐cell. Cell division starts once certain peptidoglycan enzymes and their activators have moved to the FtsZ‐ring. Gram‐negative bacteria like Escherichia coli simultaneously synthesize and cleave the septum peptidoglycan during division leading to a constriction. The outer membrane constricts together with the peptidoglycan layer with the help of the transenvelope spanning Tol–Pal system.
The peptidoglycan layer is responsible for maintaining bacterial cell shape and permitting cell division. Cell wall growth is facilitated by peptidoglycan synthases and hydrolases and is potentially ...modulated by components of the central carbon metabolism. In Bacillus subtilis, UgtP synthesises the glucolipid precursor for lipoteichoic acid and has been suggested to function as a metabolic sensor governing cell size. Here we show that ugtP mutant cells have increased levels of cell wall precursors and changes in their peptidoglycan that suggest elevated DL-endopeptidase activity. The additional deletion of lytE, encoding a DL-endopeptidase important for cell elongation, in the ugtP mutant background produced cells with severe shape defects. Interestingly, the ugtP lytE mutant recovered normal rod-shape by acquiring mutations that decreased the expression of the peptidoglycan synthase PBP1. Together our results suggest that cells lacking ugtP must re-adjust the balance between peptidoglycan synthesis and hydrolysis to maintain proper cell morphology.
Peptidoglycan hydrolases contribute to the generation of helical cell shape in Campylobacter and Helicobacter bacteria, while cytoskeletal or periskeletal proteins determine the curved, vibrioid cell ...shape of Caulobacter and Vibrio. Here, we identify a peptidoglycan hydrolase in the vibrioid-shaped predatory bacterium Bdellovibrio bacteriovorus which invades and replicates within the periplasm of Gram-negative prey bacteria. The protein, Bd1075, generates cell curvature in B. bacteriovorus by exerting LD-carboxypeptidase activity upon the predator cell wall as it grows inside spherical prey. Bd1075 localizes to the outer convex face of B. bacteriovorus; this asymmetric localization requires a nuclear transport factor 2-like (NTF2) domain at the protein C-terminus. We solve the crystal structure of Bd1075, which is monomeric with key differences to other LD-carboxypeptidases. Rod-shaped Δbd1075 mutants invade prey more slowly than curved wild-type predators and stretch invaded prey from within. We therefore propose that the vibrioid shape of B. bacteriovorus contributes to predatory fitness.
PDF
