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 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 The mericarp of the halophyte Crithmum maritimum (Apiaceae): structural features, germination, and salt distribution

Biologia ◽  
2010 ◽  
Vol 65 (3) ◽  
Author(s):  
Abdallah Atia ◽  
Ahmed Debez ◽  
Zouhaier Barhoumi ◽  
Ettore Pacini ◽  
Chedly Abdelly ◽  
...  
Keyword(s):  
Structural Features ◽  
Protective Role ◽  
Salt Leaching ◽  
Salt Ions ◽  
Wide Range ◽  
Secretory Canals ◽  
Seed Fall ◽  
Salt Distribution ◽  
Hostile Environments

AbstractAt maturation and during seed fall and dispersal, halophyte seeds may be subjected to invasion by salt ions. How these seeds remain viable in such hostile environments is however still unclear, depending for instance on the species and the family. In the Apiaceae, the mericarp (fruit) shows a wide range of morphological and anatomical modifications, many of which may enhance the adaptation to severe environmental conditions. Therefore, structural features, ion accumulation, and long-term floating capacity were investigated in the fruit (mericarp) of the halophyte Crithmum maritimum L. The mericarp was composed of a spongy outer coat, a secretory envelope, a thin endocarp reduced to a unicellular layer delimiting the endosperm, and an embryo. Both of the secretory canals and the endocarp adhered after complete ripening of the mericarp, while the epicarp and much of the mesocarp formed the spongy coat. Assessing long-term floating ability of the fruit under laboratory conditions revealed that even after 60 d, more than 98% of C. maritimum L. mericarps still floated over seawater. Seed germination was delayed and reduced by the spongy coat. The X-ray microanalysis revealed that the spongy coat and the secretory canals contained essentially Cl and Na, while seeds, i.e. endosperm and embryo, accumulated mostly Mg, K and P. In a subsequent experiment designed to simulate salt leaching by rain, most of the salt accumulated in the spongy coat and seeds was released after 2 h imbibition in distilled water. Taken together, these results highlight the protective role of the mericarp and the likely involvement of this structure in the seed dispersal of C. maritimum L. This may ultimately have eco-physiological implications explaining the successful establishment of this halophyte in its native saline biotopes.

A Mutation in Paramecium tetraurelia Reveals Functional and Structural Features of Developmentally Excised DNA Elements

Genetics ◽  
1998 ◽  
Vol 148 (1) ◽  
pp. 139-149 ◽  
Author(s):  
Kimberly M Mayer ◽  
Kazuyuki Mikami ◽  
James D Forney
Keyword(s):  
Mutant Cell ◽  
Consensus Sequence ◽  
Surface Protein ◽  
Structural Features ◽  
Inverted Terminal Repeat ◽  
Paramecium Tetraurelia ◽  
Coding Region ◽  
Conserved Sequence ◽  
Variable Surface ◽  
Dna Elements

Abstract The excision of internal eliminated sequences (IESs) from the germline micronuclear DNA occurs during the differentiation of a new macronuclear genome in ciliated protozoa. In Paramecium, IESs are generally short (28–882 bp), AT rich DNA elements that show few conserved sequence features with the exception of an inverted-terminal-repeat consensus sequence that has similarity to the ends of mariner/Tc1 transposons (Klobutcher and Herrick 1995). We have isolated and analyzed a mutant cell line that cannot excise a 370-bp IESs (IES2591) from the coding region of the 51A variable surface protein gene. A single micronuclear C to T transition within the consensus sequence prevents excision. The inability to excise IES2591 has revealed a 28-bp IES inside the larger IES, suggesting that reiterative integration of these elements can occur. Together, the consensus sequence mutation and the evidence for reiterative integration support the theory that Paramecium IESs evolved from transposable elements. Unlike a previously studied Paramecium IES, the presence of this IES in the macronucleus does not completely inhibit excision of its wild-type micronuclear copy through multiple sexual generations.

scholarly journals Susceptibility of Clinical Isolates of Burkholderia pseudomallei to a Lipid A Biosynthesis Inhibitor

2017 ◽  
Vol 97 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Sineenart Sengyee ◽  
Natnaree Saiprom ◽  
Suporn Paksanont ◽  
Direk Limmathurotsakul ◽  
Vanaporn Wuthiekanun ◽  
...  
Keyword(s):  
Burkholderia Pseudomallei ◽  
Lipid A ◽  
Clinical Isolates ◽  
Biosynthesis Inhibitor ◽  
Lipid A Biosynthesis

scholarly journals Phosphoglycolipid Profiling of Bacterial Endotoxins

2018 ◽  
Vol 46 (1) ◽  
pp. 7-11 ◽  
Author(s):  
Anikό Kilár ◽  
Ágnes Dornyel ◽  
Viktor Sándor ◽  
Ferenc Kilár ◽  
Béla Kocsis
Keyword(s):  
Lipid A ◽  
De Novo ◽  
Clinical Symptoms ◽  
Phosphorylation Site ◽  
Reversed Phase ◽  
Fatty Acyl ◽  
Structural Elucidation ◽  
Bacterial Endotoxins ◽  
Product Ions ◽  
Tandem Mass Spectrometric

Abstract Much interest is at present focused on bacterial endotoxins, also known as lipopolysaccharides (LPS), as they are responsible for the development of clinical symptoms of Gram-negative sepsis which is the leading cause of death in intensive care units. Endotoxicity is associated with the special phosphoglycolipid part of LPS, termed lipid A. Main challenges in the structural elucidation of lipid A arise from its amphiphilic character and inherent heterogeneity. A mass spectrometrybased de novo method combined with reversed-phase liquid chromatography for the detailed structural characterization of complex lipid A mixtures (obtained by mild acid hydrolysis of LPS) from different bacterial sources has been developed. Tandem mass spectrometric measurements were performed with an electrospray-ionisation quadrupole time-of-flight (ESI-Q-TOF) mass spectrometer in both negative- and positive-ionization modes in order to explore fragmentation pathways. It was found that characteristic product ions in the positive-ion mode could be used for the unambiguous assignment of the phosphorylation site, whereas the use of both ionization modes provided consistent and/or complementary information about the fatty acyl distribution between the two glucosamine moieties of lipid A. Since the immunostimulatory (advantageous) vs. proinflammatory (endotoxic) effect of the lipid A is closely related to the fine chemical structure, our relatively simple structural elucidation strategy could offer great potential in the bioanalysis of native lipid A samples and lipid A-based vaccines

Water and solute permeability of rat lung caveolae: high permeabilities explained by acyl chain unsaturation

2005 ◽  
Vol 289 (1) ◽  
pp. C33-C41 ◽  
Author(s):  
Warren G. Hill ◽  
Eyad Almasri ◽  
W. Giovanni Ruiz ◽  
Gerard Apodaca ◽  
Mark L. Zeidel
Keyword(s):  
Water Permeability ◽  
Acyl Chain ◽  
Water Flux ◽  
High Water ◽  
Fatty Acyl ◽  
Rat Lung ◽  
Membrane Structures ◽  
Solute Permeability ◽  
Outer Leaflet ◽  
Osmotic Water

Caveolae are invaginated membrane structures with high levels of cholesterol, sphingomyelin, and caveolin protein that are predicted to exist as liquid-ordered domains with low water permeability. We isolated a caveolae-enriched membrane fraction without detergents from rat lung and characterized its permeability properties to nonelectrolytes and protons. Membrane permeability to water was 2.85 ± 0.41 × 10−3 cm/s, a value 5–10 times higher than expected based on comparisons with other cholesterol and sphingolipid-enriched membranes. Permeabilities to urea, ammonia, and protons were measured and found to be moderately high for urea and ammonia at 8.85 ± 2.40 × 10−7and 6.84 ± 1.03 × 10−2 respectively and high for protons at 8.84 ± 3.06 × 10−2 cm/s. To examine whether caveolin or other integral membrane proteins were responsible for high permeabilities, liposomes designed to mimic the lipids of the inner and outer leaflets of the caveolar membrane were made. Osmotic water permeability to both liposome compositions were determined and a combined inner/outer leaflet water permeability was calculated and found to be close to that of native caveolae at 1.58 ± 1.1 × 10−3 cm/s. In caveolae, activation energy for water flux was high (19.4 kcal/mol) and water permeability was not inhibited by HgCl2; however, aquaporin 1 was detectable by immunoblotting. Immunostaining of rat lung with AQP1 and caveolin antisera revealed very low levels of colocalization. We conclude that aquaporin water channels do not contribute significantly to the observed water flux and that caveolae have relatively high water and solute permeabilities due to the high degree of unsaturation in their fatty acyl chains.

Polyadenylation of mRNA: minimal substrates and a requirement for the 2' hydroxyl of the U in AAUAAA

1990 ◽  
Vol 10 (4) ◽  
pp. 1705-1713
Author(s):  
P L Wigley ◽  
M D Sheets ◽  
D A Zarkower ◽  
M E Whitmer ◽  
M Wickens
Keyword(s):  
Cleavage Site ◽  
Structural Features ◽  
Single Nucleotide ◽  
Conserved Sequence ◽  
Specificity Factor

mRNA-specific polyadenylation can be assayed in vitro by using synthetic RNAs that end at or near the natural cleavage site. This reaction requires the highly conserved sequence AAUAAA. At least two distinct nuclear components, an AAUAAA specificity factor and poly(A) polymerase, are required to catalyze the reaction. In this study, we identified structural features of the RNA substrate that are critical for mRNA-specific polyadenylation. We found that a substrate that contained only 11 nucleotides, of which the first six were AAUAAA, underwent AAUAAA-specific polyadenylation. This is the shortest substrate we have used that supports polyadenylation: removal of a single nucleotide from either end of this RNA abolished the reaction. Although AAUAAA appeared to be the only strict sequence requirement for polyadenylation, the number of nucleotides between AAUAAA and the 3' end was critical. Substrates with seven or fewer nucleotides beyond AAUAAA received poly(A) with decreased efficiency yet still bound efficiently to specificity factor. We infer that on these shortened substrates, poly(A) polymerase cannot simultaneously contact the specificity factor bound to AAUAAA and the 3' end of the RNA. By incorporating 2'-deoxyuridine into the U of AAUAAA, we demonstrated that the 2' hydroxyl of the U in AAUAAA was required for the binding of specificity factor to the substrate and hence for poly(A) addition. This finding may indicate that at least one of the factors involved in the interaction with AAUAAA is a protein.

The Protective Role of Toll-Like Receptor Agonist Monophosphoryl Lipid A Against Vaccinated Murine Schistosomiasis

2020 ◽  
Vol 65 (3) ◽  
pp. 652-660
Author(s):  
Ibrahim Aly ◽  
Essam H. Ibrahim ◽  
Rabab S. Hamad ◽  
Hoda E. L. Sayed ◽  
Sama M. N. Attiyah ◽  
...  
Keyword(s):  
Receptor Agonist ◽  
Lipid A ◽  
Protective Role ◽  
Toll Like Receptor ◽  
Monophosphoryl Lipid A ◽  
Monophosphoryl Lipid

scholarly journals The Pea Nodule Environment Restores the Ability of a Rhizobium leguminosarum Lipopolysaccharide acpXL Mutant To Add 27-Hydroxyoctacosanoic Acid to Its Lipid A

2006 ◽  
Vol 188 (6) ◽  
pp. 2126-2133 ◽  
Author(s):  
Vinata Vedam ◽  
Elmar Kannenberg ◽  
Anup Datta ◽  
Dusty Brown ◽  
Janine G. Haynes-Gann ◽  
...  
Keyword(s):  
Salt Concentration ◽  
Rhizobium Leguminosarum ◽  
Lipid A ◽  
Root Nodule ◽  
Fatty Acyl ◽  
Alternative Mechanism ◽  
Acyl Residue ◽  
Host Root ◽  
Physiological Properties ◽  
Alternate Mechanism

ABSTRACT Members of the Rhizobiaceae contain 27-hydroxyoctacosanoic acid (27OHC28:0) in their lipid A. A Rhizobium leguminosarum 3841 acpXL mutant (named here Rlv22) lacking a functional specialized acyl carrier lacked 27OHC28:0 in its lipid A, had altered growth and physiological properties (e.g., it was unable to grow in the presence of an elevated salt concentration [0.5% NaCl]), and formed irregularly shaped bacteroids, and the synchronous division of this mutant and the host plant-derived symbiosome membrane was disrupted. In spite of these defects, the mutant was able to persist within the root nodule cells and eventually form, albeit inefficiently, nitrogen-fixing bacteroids. This result suggested that while it is in a host root nodule, the mutant may have some mechanism by which it adapts to the loss of 27OHC28:0 from its lipid A. In order to further define the function of this fatty acyl residue, it was necessary to examine the lipid A isolated from mutant bacteroids. In this report we show that addition of 27OHC28:0 to the lipid A of Rlv22 lipopolysaccharides is partially restored in Rlv22 acpXL mutant bacteroids. We hypothesize that R. leguminosarum bv. viciae 3841 contains an alternate mechanism (e.g., another acp gene) for the synthesis of 27OHC28:0, which is activated when the bacteria are in the nodule environment, and that it is this alternative mechanism which functionally replaces acpXL and is responsible for the synthesis of 27OHC28:0-containing lipid A in the Rlv22 acpXL bacteroids.

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