scholarly journals Aminosugar-based immunomodulator lipid A: synthetic approaches

2018 ◽  
Vol 14 ◽  
pp. 25-53 ◽  
Author(s):  
Alla Zamyatina
Keyword(s):  
Lipid A ◽  
Germ Line ◽  
Bacterial Species ◽  
Complex Mixture ◽  
Structural Heterogeneity ◽  
Structural Features ◽  
Innate Immune ◽  
Outer Leaflet ◽  
Innate Immune Signaling ◽  
Biological Studies

The immediate immune response to infection by Gram-negative bacteria depends on the structure of a lipopolysaccharide (LPS, also known as endotoxin), a complex glycolipid constituting the outer leaflet of the bacterial outer membrane. Recognition of picomolar quantities of pathogenic LPS by the germ-line encoded Toll-like Receptor 4 (TLR4) complex triggers the intracellular pro-inflammatory signaling cascade leading to the expression of cytokines, chemokines, prostaglandins and reactive oxygen species which manifest an acute inflammatory response to infection. The “endotoxic principle” of LPS resides in its amphiphilic membrane-bound fragment glycophospholipid lipid A which directly binds to the TLR4·MD-2 receptor complex. The lipid A content of LPS comprises a complex mixture of structural homologs varying in the acylation pattern, the length of the (R)-3-hydroxyacyl- and (R)-3-acyloxyacyl long-chain residues and in the phosphorylation status of the β(1→6)-linked diglucosamine backbone. The structural heterogeneity of the lipid A isolates obtained from bacterial cultures as well as possible contamination with other pro-inflammatory bacterial components makes it difficult to obtain unambiguous immunobiological data correlating specific structural features of lipid A with its endotoxic activity. Advanced understanding of the therapeutic significance of the TLR4-mediated modulation of the innate immune signaling and the central role of lipid A in the recognition of LPS by the innate immune system has led to a demand for well-defined materials for biological studies. Since effective synthetic chemistry is a prerequisite for the availability of homogeneous structurally distinct lipid A, the development of divergent and reproducible approaches for the synthesis of various types of lipid A has become a subject of considerable importance. This review focuses on recent advances in synthetic methodologies toward LPS substructures comprising lipid A and describes the synthesis and immunobiological properties of representative lipid A variants corresponding to different bacterial species. The main criteria for the choice of orthogonal protecting groups for hydroxyl and amino functions of synthetically assembled β(1→6)-linked diglucosamine backbone of lipid A which allows for a stepwise introduction of multiple functional groups into the molecule are discussed. Thorough consideration is also given to the synthesis of 1,1′-glycosyl phosphodiesters comprising partial structures of 4-amino-4-deoxy-β-L-arabinose modifiedBurkholderialipid A and galactosamine-modifiedFrancisella lipid A. Particular emphasis is put on the stereoselective construction of binary glycosyl phosphodiester fragments connecting the anomeric centers of two aminosugars as well as on the advanced P(III)-phosphorus chemistry behind the assembly of zwitterionic double glycosyl phosphodiesters.

scholarly journals Human TLR4 and noncanonical inflammasome differ in their ability to respond to distinct lipid A variants

2021 ◽  
Author(s):  
Jasmine Alexander-Floyd ◽  
Antonia R. Bass ◽  
Erin M. Harberts ◽  
Daniel Grubaugh ◽  
Joseph D. Buxbaum ◽  
...  
Keyword(s):  
Lipid A ◽  
Inflammatory Responses ◽  
Bacterial Species ◽  
Acyl Chain ◽  
Innate Immune ◽  
Core Oligosaccharide ◽  
Phosphorylation State ◽  
Tlr4 Activation ◽  
Bacterial Lipid ◽  
Immune Detection

Detection of Gram-negative bacterial lipid A by the extracellular sensor, MD-2/TLR4 or the intracellular inflammasome sensors, CASP4 and CASP5, induces robust inflammatory responses. The chemical structure of lipid A, specifically the phosphorylation and acylation state, varies across and within bacterial species, potentially allowing pathogens to evade or suppress host immunity. Currently, it is not clear how distinct alterations in the phosphorylation or acylation state of lipid A affect both human TLR4 and CASP4/5 activation. Using a panel of engineered lipooligosaccharides (LOS) derived from Yersinia pestis with defined lipid A structures that vary in their acylation or phosphorylation state, we identified that differences in phosphorylation state did not affect TLR4 or CASP4/5 activation. However, the acylation state differentially impacted TLR4 and CASP4/5 activation. Specifically, all of the examined tetra-, penta-, and hexa-acylated LOS variants activated CASP4/5-dependent responses, whereas TLR4 responded to penta- and hexa-acylated LOS but did not respond to tetra-acylated LOS or penta-acylated LOS lacking the secondary acyl chain at the 3' position. As expected, lipid A alone was sufficient for TLR4 activation; however, human macrophages required both lipid A and the core oligosaccharide to mount a robust CASP4/5 inflammasome response. Our findings show that human TLR4 and CASP4/5 detect both shared and non-overlapping LOS/lipid A structures, which enables the innate immune system to recognize a wider range of bacterial LOS/lipid A, thereby constraining the ability of pathogens to evade innate immune detection.

The outer membrane glycolipids of bacteria from cold environments: isolation, characterization, and biological activity

2019 ◽  
Vol 95 (7) ◽  
Author(s):  
Angela Casillo ◽  
Ermenegilda Parrilli ◽  
Maria Luisa Tutino ◽  
Maria Michela Corsaro
Keyword(s):  
Biological Activity ◽  
Outer Membrane ◽  
Lipid A ◽  
Structural Heterogeneity ◽  
Structural Features ◽  
Cold Adapted ◽  
Bacterial Membranes ◽  
Cold Environments ◽  
Main Components ◽  
Structural Adaptations

ABSTRACTLipopolysaccharides (LPSs) are the main components of the external leaflet of the outer membrane of Gram-negative bacteria. Microorganisms that colonize permanently or transiently cold habitats have evolved an array of structural adaptations, some of which involve components of bacterial membranes. These adaptations assure the perfect functionality of the membrane even at freezing or sub-freezing growth temperatures. This review summarizes the state-of-the-art information concerning the structural features of the LPSs produced by cold-adapted bacteria. The LPS structure has recently been elucidated from species mainly belonging to Gammaproteobacteria and Flavobacteriaceae. Although the reported structural heterogeneity may arise from the phylogenetic diversity of the analyzed source strains, some generalized trends can be deduced. For instance, it is clear that only a small portion of LPSs displays the O-chain. In addition, the biological activity of the lipid A portion from several cold-adapted strains is reported.

scholarly journals The structure of lipopolysaccharide transport protein B (LptB) from Burkholderia pseudomallei

2019 ◽  
Vol 75 (4) ◽  
pp. 227-232 ◽  
Author(s):  
Genady Pankov ◽  
Alice Dawson ◽  
William N. Hunter
Keyword(s):  
Burkholderia Pseudomallei ◽  
Lipid A ◽  
Structural Features ◽  
Protective Role ◽  
Fatty Acyl ◽  
Cell Integrity ◽  
Conserved Sequence ◽  
Outer Leaflet ◽  
Fixed Structure ◽  
Hostile Environments

The thick outer membrane (OM) of Gram-negative bacteria performs an important protective role against hostile environments, supports cell integrity, and contributes to surface adhesion and in some cases also to virulence. A major component of the OM is lipopolysaccharide (LPS), a complex glycolipid attached to a core containing fatty-acyl chains. The assembly and transport of lipid A, the membrane anchor for LPS, to the OM begins when a heteromeric LptB2FG protein complex extracts lipid A from the outer leaflet of the inner membrane. This process requires energy, and upon hydrolysis of ATP one component of the heteromeric assembly, LptB, triggers a conformational change in LptFG in support of lipid A transport. A structure of LptB from the intracellular pathogen Burkholderia pseudomallei is reported here. LptB forms a dimer that displays a relatively fixed structure irrespective of whether it is in complex with LptFG or in isolation. Highly conserved sequence and structural features are discussed that allow LptB to fuel the transport of lipid A.

scholarly journals Position-specific secondary acylation determines detection of lipid A by murine TLR4 and caspase-11

2021 ◽  
Author(s):  
Erin M Harberts ◽  
Daniel Grubaugh ◽  
Daniel C. Akuma ◽  
Sunny Shin ◽  
Robert K Ernst ◽  
...  
Keyword(s):  
Lipid A ◽  
Inflammatory Responses ◽  
Chemical Space ◽  
Bacterial Species ◽  
Direct Analysis ◽  
Structural Features ◽  
Gram Negative ◽  
Acyl Chains ◽  
Immune Sensing ◽  
Bacterial Lipid

Immune sensing of the Gram-negative bacterial membrane glycolipid lipopolysaccharide (LPS) is both a critical component of host defense against Gram-negative bacterial infection, and a contributor to hyper-inflammatory response, leading to sepsis and death. Innate immune activation by LPS is due to the lipid A moiety, an acylated di-glucosamine molecule that can activate inflammatory responses via the extracellular sensor TLR4/MD2 or the cytosolic sensor caspase-11 (Casp11). The number and length of acyl chains present on bacterial lipid A structures vary across bacterial species and strains, which affects the magnitude of TLR4 and Casp11 activation. TLR4 and Casp11 are thought to respond similarly to various lipid A structures, as tetra-acylated lipid A structures do not activate either sensor, whereas hexa-acylated structures activate both sensors. However, direct analysis of extracellular and cytosolic responses to the same sources and preparations of LPS/lipid A structures have been limited, and the precise features of lipid A that determine the differential activation of each receptor remain poorly defined. To address this question, we used rationally engineered lipid A isolated from a series of bacterial acyl-transferase mutants that produce novel, structurally defined molecules. Intriguingly, we find that the location of specific secondary acyl chains on lipid A resulted in differential recognition by TLR4- or Casp11, providing new insight into the structural features of lipid A required to activate either TLR4- or Casp11. Our findings indicate that TLR4 and Casp11 sense non-overlapping areas of lipid A chemical space, thereby constraining the ability of Gram-negative pathogens to evade innate immunity.

scholarly journals Hexa-Acylated Lipid A Is Required for Host Inflammatory Response to Neisseria gonorrhoeae in Experimental Gonorrhea

2013 ◽  
Vol 82 (1) ◽  
pp. 184-192 ◽  
Author(s):  
Xiyou Zhou ◽  
Xi Gao ◽  
Peter M. Broglie ◽  
Chahnaz Kebaier ◽  
James E. Anderson ◽  
...  
Keyword(s):  
Neisseria Gonorrhoeae ◽  
Lipid A ◽  
Innate Immune ◽  
Immune Recognition ◽  
Toll Like Receptor ◽  
Inflammatory Signaling ◽  
Toll Like Receptor 4 ◽  
Immune Signaling ◽  
Content Type ◽  
Innate Immune Signaling

ABSTRACTNeisseria gonorrhoeaecauses gonorrhea, a sexually transmitted infection characterized by inflammation of the cervix or urethra. However, a significant subset of patients withN. gonorrhoeaeremain asymptomatic, without evidence of localized inflammation. Inflammatory responses toN. gonorrhoeaeare generated by host innate immune recognition ofN. gonorrhoeaeby several innate immune signaling pathways, including lipooligosaccharide (LOS) and other pathogen-derived molecules through activation of innate immune signaling systems, including toll-like receptor 4 (TLR4) and the interleukin-1β (IL-1β) processing complex known as the inflammasome. The lipooligosaccharide ofN. gonorrhoeaehas a hexa-acylated lipid A.N. gonorrhoeaestrains that carry an inactivatedmsbB(also known aslpxL1) gene produce a penta-acylated lipid A and exhibit reduced biofilm formation, survival in epithelial cells, and induction of epithelial cell inflammatory signaling. We now show thatmsbB-deficientN. gonorrhoeaeinduces less inflammatory signaling in human monocytic cell lines and murine macrophages than the parent organism. The penta-acylated LOS exhibits reduced toll-like receptor 4 signaling but does not affectN. gonorrhoeae-mediated activation of the inflammasome. We demonstrate thatN. gonorrhoeaemsbBis dispensable for initiating and maintaining infection in a murine model of gonorrhea. Interestingly, infection withmsbB-deficientN. gonorrhoeaeis associated with less localized inflammation. Combined, these data suggest that TLR4-mediated recognition ofN. gonorrhoeaeLOS plays an important role in the pathogenesis of symptomatic gonorrhea infection and that alterations in lipid A biosynthesis may play a role in determining symptomatic and asymptomatic infections.

scholarly journals TRIM5 Retroviral Restriction Activity Correlates with the Ability To Induce Innate Immune Signaling

2015 ◽  
Vol 90 (1) ◽  
pp. 308-316 ◽  
Author(s):  
Josefina Lascano ◽  
Pradeep D. Uchil ◽  
Walther Mothes ◽  
Jeremy Luban
Keyword(s):  
Germ Line ◽  
Cellular Protein ◽  
Innate Immune ◽  
Primate Species ◽  
Past Infection ◽  
Immune Signaling ◽  
Susceptible Host ◽  
Retroviral Transduction ◽  
Innate Immune Signaling ◽  
Hiv 1

ABSTRACTHost restriction factor TRIM5 inhibits retroviral transduction in a species-specific manner by binding to and destabilizing the retroviral capsid lattice before reverse transcription is completed. However, the restriction mechanism may not be that simple since TRIM5 E3 ubiquitin ligase activity, the proteasome, autophagy, and TAK1-dependent AP-1 signaling have been suggested to contribute to restriction. Here, we show that, among a panel of seven primate and Carnivora TRIM5 orthologues, each of which has potential for potent retroviral restriction activity, all activated AP-1 signaling. In contrast, TRIM family paralogues most closely related to TRIM5 did not. While each primate species has a single TRIM5 gene, mice have at least seven TRIM5 homologues that cluster into two groups, Trim12a, -b, and -c and Trim30a, -b, -c, and -d. The three Trim12 proteins activated innate immune signaling, while the Trim30 proteins did not, though none of the murine Trim5 homologues restricted any of a panel of cloned retroviruses. To determine if any mouse TRIM5 homologues had potential for restriction activity, each was fused to the human immunodeficiency virus type 1 (HIV-1) CA binding protein cyclophilin A (CypA). The three Trim12-CypA fusions all activated AP-1 and restricted HIV-1 transduction, whereas the Trim30-CypA fusions did neither. AP-1 activation and HIV-1 restriction by the Trim12-CypA fusions were inhibited by disruption of TAK1. Overall then, these experiments demonstrate that there is a strong correlation between TRIM5 retroviral restriction activity and the ability to activate TAK1-dependent innate immune signaling.IMPORTANCEThe importance of retroviruses for the evolution of susceptible host organisms cannot be overestimated. Eight percent of the human genome is retrovirus sequence, fixed in the germ line during past infection. Understanding how metazoa protect their genomes from mutagenic retrovirus infection is therefore of fundamental importance to biology. TRIM5 is a cellular protein that protects host genome integrity by disrupting the retroviral capsid as it transports viral nucleic acid to the host cell nucleus. Previous data suggest that innate immune signaling contributes to TRIM5-mediated restriction. Here, we show that activation of innate immune signaling is conserved among primate and carnivore TRIM5 orthologues and among 3 of the 7 mouse Trim5 homologues and that such activity is required for TRIM5-mediated restriction activity.

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