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Pathogenicity and Virulence
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
On their part, Gram-negative pathogens have evolved structural modifications to counteract their vulnerability to the complement system. Inhibition of activation of the alternate complement pathway by various capsules and by abequose in the O polysaccharide of S. typhymurium has been mentioned. In other instances complement activation occurs, but the bacterium escapes destruction by the membrane attack complex. For example, some Salmonella strains possess unusually long O polysaccharide chains that function as steric barriers to the insertion of the membrane attack complex into the outer membrane. N. gonorrhoeae and certain pathogenic strains of E. coli possess outer membrane proteins that either prevent the insertion of the membrane attack complex or cause its rapid release.
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
Polysaccharide modification by glycosyl and non-carbohydrate substituents may be stoichiometric or nonstoichiometric, and the difference most likely lies in the stage of biosynthesis at which the substitution reaction occurs. In the case of Salmonella serogroups E and B, in vitro and in vivo studies have both shown that incorporation of the stoichiometric side-branch sugars occurs prior to completion of the O unit and the subsequent polymerization reactions. Studies with sero-group B strains unable to produce the side chain precursor, CDP-abequose, fail to produce O-PS (56). The donor for nonstoichiometric glucosyl substituents in S. enterica O-PSs is an unusual lipid intermediate, a-glucosylmonophosphorylundecaprenol (57–59). In sero-groups B and D, glucosylation occurs postpolymerization and is assumed to occur at the level of the O-hapten (Und-PP-linked O-PS) (58–61). In contrast, in serogroups Cl and C2, glucosylation occurs before polymerization, at the level of individual Und-PP-linked O units (62). O-Acetylation has been studied in S. enterica serogroup El both in vivo (63) and in vitro (64). The donor for the acetyl group is acetyl-CoA, and the substrate for the acetyltransferase reaction is the single Und-PP-linked O unit.
Molecular Aspects of Anti-Polysaccharide Antibody Responses
Published in Maurizio Zanetti, J. Donald Capra, The Antibodies, 2002
Kurt Brorson, Pablo Garcia-Ojeda, Kathryn E. Stein
The Sel55-4:O-antigen structure has been resolved to 2.05A (VH119.13:VX1; [20]). Sel55 binds a trisaccharide epitope, aD-Gal(1: 2)[aD-Abe(1: 3)]aD-Man of the O-antigen with relatively low affinity (2 X 105 M_1). The 304 A2 binding site consists of both a shallow cavity (8 A deep by 7 A wide) and surface residues. The abequose branch side chain of the PS is accommodated by the shallow cavity, while the Man and Gal sugars lie perpendicular to the VH:VL interface. Thus, this antibody is neither "groove-type" nor "cavity-type", but a combination of both. Contact with antigen is dominated by H-bonds with aromatic residues (His 97H, His 35H, His 32L, Trp 95L, Trp 91L, Tyr 99H) and hydrophobic interactions. The H1, H3, L1 and L3 loops of the antibody participate in antigen contact, with about 60% of the contact surface comprised of VH residues. A high degree of specificity of the antibody probably results in part from a buried water molecule that coordinates four hydrogen bonds with the abequose and the CDR surface, a sterically demanding interaction.
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
We also investigated the presence of active enzymes in the metagenomes of the microbiota before diet change (D0) and on D28 after the diet change in both groups (Figure 4). The relative abundances of auxiliary activities (AAs p =.68) carbohydrate-binding modules (CBMs p =.17) carbohydrate esterases (CEs p =.33) glycoside hydrolases (GHs p =.16) and glycosyltransferases (GTs) (p=.096 Figure 4a) were similar at D0 between the mice fed an ISO or PF diet. However mice fed an ISO diet had significantly higher polysaccharide lyase (PL) activity along with a reduction in the activity of S-layer homology domains (SLHs; Figure 4b 4c). No significant changes in the relative abundances of AAs CBMs CEs and GHs were observed on D28 after diet change between the groups. Yet there was a significant reduction in GT activity when the diet was changed from ISO to PF (Figure 4d). Within GTs only GT2_glyco_tranf_2 activity was significantly higher on D28 in mice in which the diet changed from PF to ISO compared to mice in which the diet changed from ISO to PF (p =.00045). The GT2 family of enzymes are diverse and are involved in transferring the sugar from UDP-glucose UDP-N-acetyl- galactosamine GDP-mannose or CDP-abequose to a range of substrates including cellulose dolichol phosphate and teichoic acids (https://pfam.xfam.org/family/PF00535) which form the building blocks of LPSs implying that ISO dietary conditions may contribute to formation of structurally different LPS compared to a PF diet. Similarly the relative abundance of PL activity was significant on D28 when the diet was changed to PF from ISO but the change was also evident on D0 indicating that PLs were not affected overall by the change in diet (Figure 4e). The significantly high SLH activity at D0 in mice fed a PF diet was lost by D28 when the diet was changed to ISO (Figure 4f) suggesting that the ISO diet reduces SLH activity. SLHs are shown to mediate the binding of exocellular proteins to the cell surface in vivo and in vitro29–31 and thus can affect cellular signaling. Taken together differences in active carbohydrate enzymatic activity after dietary change suggest differences in LPS and exocellular protein composition and structure of the microbiota.