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Escherichia
Published in Dongyou Liu, Laboratory Models for Foodborne Infections, 2017
Capsule and outer membrane. The outer membrane of E. coli is composed of a lipid bilayer, which in turn consists of a phospholipid inner leaflet and an LPS outer leaflet, together with several kinds of membrane proteins in the periplasm (the space between the inner and outer leaflets/membranes). In the outer membrane, a glycolipid (called the enterobacterial common antigen or ECA) is found in E. coli. In some E. coli strains, the outer membrane is covered by a polysaccharide capsule containing K antigens. Under conditions of high osmolarity, low temperature, and low humidity, other polysaccharides such as M antigens (colanic acids, which are polymers of glucose, galactose, fucose, and galacturonic acid) are synthesized.
Genetics and Biosynthesis of Lipopolysaccharide O-Antigens
Published in Helmut Brade, Steven M. Opal, Stefanie N. Vogel, David C. Morrison, Endotoxin in Health and Disease, 2020
Wendy J. Keenleyside, Chris Whitfield
Although the role of lipid A core as the anchor for O antigens has been well established for decades, the distinction of what may be considered an O antigen has become complicated by more recent studies. In E. coli, for example, lipid A core can act as an anchor for several different polysaccharides. Enterobacterial common antigen (ECA) is expressed by virtually every member of the Enterobacteriaceae. Although normally anchored by phospholipid, ECA can be found attached to lipid A core in strains that do not synthesize a typical O antigen (9). Similarly, the group I capsular K antigens of E. coli exist in both a lipid A core-bound form (known as KLPS) as well as a high molecular weight LPS-free capsular form (10–14). These K antigens are co-expressed with an O antigen, and the designation of each polymer as the O or K antigen is operationally (serology) based (see Ref. 10). This versatility of lipid A core as an anchor is not confined to E. coli. In Salmonella strains, lipid A core may serve as an acceptor for the classical O antigen as well as the minor antigens T1 and T2 (15), and among members of the 0:54 Salmonella serogroup, two structurally distinct O polysaccharides compete for the same lipid A core acceptor (see below). Serratia marcescens serotype 016 expresses two structurally distinct lipid A core-bound polymers: the serotype 016 O antigen and a riban homopolymer, which has the same structure as the T1 antigen of Salmonella (16). Among nonenteric bacteria, Pseudomonas aeruginosa also expresses two lipid A core-linked polymers. One is a conserved polyrham-nose homopolymer known as A-band LPS (Table 1), which is analogous to lipid A core-linked ECA. The other is the serotype-specific heteropolymer known as B-band LPS (reviewed in Ref. 17). Interestingly, while both O-polysaccharides are attached to lipid A core, preliminary evidence suggests that the outer core structures of the two LPS are different (18,19).
Dietary Isoflavones Alter Gut Microbiota and Lipopolysaccharide Biosynthesis to Reduce Inflammation
Published in Gut Microbes, 2022
Sudeep Ghimire, Nicole M. Cady, Peter Lehman, Stephanie R. Peterson, Shailesh K. Shahi, Faraz Rashid, Shailendra Giri, Ashutosh K. Mangalam
On D28 the diet change from ISO to PF enriched the following biosynthesis pathways compared to D0: lactose and galactose degradation pyruvate fermentation inosine-5’ phosphate biosynthesis UDP-N-acetyl-D-glucosamine biosynthesis I and O-antigen building block biosynthesis (Figure 5c). UDP-N-acetyl-D-glucosamine is the precursor of cell wall peptidoglycan LPS and enterobacterial common antigen. Similarly the O-antigen specific chains are a part of LPSs that are known to evoke a specific immune response. Thus it appears that the diet switch from ISO to PF enhances LPS biosynthesis in the gut to induce an immune response. However enrichment of no such LPS biosynthesis pathway was observed when the diet was changed from ISO to PF on D28 when compared to D0. The differences in the carbohydrate enzymatic activity that we observed after dietary change could change the LPS and exocellular protein structure produced by the microbiota. Thus LPS synthesis may be altered because of dietary ISO or PF conditions after changes in the diet. In fact the differences in the gut microbiota have been previously described to affect immune signaling and immunogenicity in humans because of differences in LPS.32 Also we observed enrichment of methionine aspartate and lysine pathways along with glycolysis and non-oxidant pentose phosphate pathways on D28 compared to D0 when the diet was switched from PF to ISO (Figure 5d). This indicates that changing the diet to one that is PF alters the functions of the gut microbiota and may promote the synthesis of LPS-based antigenic molecules to evoke a different immune response.
A mechanistic perspective on targeting bacterial drug resistance with nanoparticles
Published in Journal of Drug Targeting, 2021
Khatereh Khorsandi, Saeedeh Keyvani-Ghamsari, Fedora Khatibi Shahidi, Reza Hosseinzadeh, Simab Kanwal
An asymmetric lipid bilayer of the outer membrane makes it an unusual structure, with an outer leaflet composed of LPS and an inner leaflet containing phospholipids [30]. LPS is glucosamine-based glycolipid including three sections: the membrane anchor lipid A, a short core oligosaccharide and a very changeable O-antigen polysaccharide [31]. Lipid A is an ‘endotoxin’ that induces the inherent immune response, enhances pro-inflammatory cytokine release and consequently produces various dramatic symptoms related to systemic Gram-negative infections such as fever and sepsis [32]. Gram-negative O-antigen commonly generates a powerful antibody reaction, which can result in a later infection [33]. Other Gram-negative outer membrane individual features involve lipoproteins and integral membrane proteins (outer membrane proteins) which are inserted in the outer membrane [34]. Receiving nutrients and discharging waste products are also functions of outer membrane proteins that have channel structures. The outer membrane can also contain other glycolipids like an enterobacterial common antigen which is specific in E. coli [35,36]. The outer membrane also has binding site for superficial organelles, such as pili, that are responsible for bacterial surface adherence [37].
Glycoconjugate vaccines: current approaches towards faster vaccine design
Published in Expert Review of Vaccines, 2019
Francesca Micoli, Linda Del Bino, Renzo Alfini, Filippo Carboni, Maria Rosaria Romano, Roberto Adamo
Glycoconjugate production in E. coli requires the presence of genome clusters encoding the bacterial polysaccharide, a plasmid encoding the carrier protein, and the oligosaccharyl transferase (OTase; typically the enzyme PglB from C. jejuni) [95]. The DNA encoding the enzymes required for N-glycosylation can also be genome-integrated by replacing, for instance, the native enterobacterial common antigen and O-polysaccharide antigen loci [96]. The system relies on the expression and assembling of glycans repeating units anchored to the lipid undecaprenyl pyrophosphate (Und-PP), which is present in the cytoplasmic membrane of E. coli. The Und-PP naturally functions as an anchor for the construction of oligo- and polysaccharides, including the O-polysaccharide antigen in Gram-negative bacteria. Then, the glycan moiety is flipped in the periplasmatic space by an ATP-binding cassette (ABC) transporter, and elongated by a polymerase (Wzy). Subsequently, the PglB transfers Und-PP-linked glycans to the target carrier protein containing the appropriate consensus acceptor sequence (i.e. D/E-X1-N-X2-S/T, where X1 and X2 can be any amino acid except proline) [97].