Mycobacterium avium glycopeptidolipids require specific acetylation and methylation patterns for signaling through toll-like receptor 2

Multiomics integration reveals NETosis heterogeneity and TLR2 as a prognostic biomarker in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant neoplasm characterized by a poor prognosis and limited therapeutic strategy. The PDAC tumor microenvironment presents a complex heterogeneity, where neutrophils emerge as the predominant constituents of the innate immune cell population. Leveraging the power of single-cell RNA-seq, spatial RNA-seq, and multi-omics approaches, we included both published datasets and our in-house patient cohorts, elucidating the inherent heterogeneity in the formation of neutrophil extracellular traps (NETs) and revealed the correlation between NETs and immune suppression. Meanwhile, we constructed a multi-omics prognostic model that suggested the patients exhibiting downregulated expression of NETs may have an unfavorable outcome. We also confirmed TLR2 as a potent prognosis factor and patients with low TLR2 expression had more effective T cells and an overall survival extension for 6 months. Targeting TLR2 might be a promising strategy to reverse immunosuppression and control tumor progression for an improved prognosis.

MA'AT Analysis: Probability Distributions of Molecular Torsion Angles in Solution from NMR Spectroscopy

ConspectusMonosaccharides adopt multiple conformations in solution, and this structural complexity increases significantly when they are assembled into oligosaccharides and polysaccharides. Characterization of the conformational properties of saccharides in solution by NMR spectroscopy has been hampered by several complicating factors, including difficulty interpreting spectra because of significant signal overlap, population averaging of NMR parameters, and unique properties of the spectra that make accurate measurements of NMR parameters prone to error (e.g., non-first-order effects on J-couplings). Current conformational assignments rely heavily on theoretical calculations, especially molecular dynamics (MD) simulations, to interpret the experimental NMR parameters. While these studies assert that the available experimental data fit the calculated models well, a lack of independent experimental validation of the force fields from which MD models are derived and an inability to test all possible models that might be compatible with the experimental data in an unbiased manner make the approach less than ideal.NMR spin couplings or J-couplings have been used as structure constraints in organic and other types of molecules for more than six decades. The dihedral angle dependence of vicinal (three-bond) 1H-1H spin couplings (3JHH) first described by Karplus led to an explosion of applications for a wide range of conformational problems. Other vicinal J-couplings (e.g., 3JCCOP, 3JHCOP, and 3JCOCH) have been found to exhibit similar dihedral angle dependencies. 3J values have been used to assign the preferred conformation in molecules that are conformationally homogeneous. However, many molecules, particularly those in biological systems, are conformationally flexible, which complicates structural interpretations of J values in solution. Three-state staggered models are often assumed in order to deconvolute the conformationally averaged J values into conformer populations. While widely applied, this approach assumes highly idealized models of molecular torsion angles that are likely to be poor representations of those found in solution. In addition, this treatment often gives negative populations and neglects the presence of librational averaging of molecular torsion angles.Recent work in this research group has focused on the development of a hybrid experimental-computational method, MA'AT analysis, that provides probability distributions of molecular torsion angles in solution that can be superimposed on those obtained by MD. Ensembles of redundant NMR spin couplings, including 3J (vicinal), 2J (geminal), and sometimes 1J (direct) values, are used in conjunction with circular statistics to provide single- and multistate models of these angles. MA'AT analysis provides accurate mean torsion angles and circular standard deviations (CSDs) of each mean angle that describe the librational motion about the angle. Both conformational equilibria and dynamics are revealed by the method. In this Account, the salient features of MA'AT analysis are discussed, including some applications to conformational problems involving saccharides and peptides.

Proteome Profile Changes Induced by Heterologous Overexpression of Mycobacterium tuberculosis-Derived Antigens PstS-1 (Rv0934) and Ag85B (Rv1886c) in Mycobacterium microti

The development of new tuberculosis vaccines remains a global priority, and recombinant vaccines are a frequently investigated option. These vaccines follow a molecular strategy that may enhance protective efficacy. However, their functional differences, particularly with respect to glycosylation, remain unknown. Recent studies have shown that glycosylation plays a key role in the host-pathogen interactions during immune recognition. The aim of this study was to determine the differences in the glycosylation profiles of two recombinant strains of Mycobacterium microti, overexpressing Ag85B (Rv1886c) and PstS-1 (Rv0934) antigens of M. tuberculosis. For each strain, the glycosylation profile was determined by Western blotting with lectins. The results showed the presence of mannosylated proteins and evidence of linked sialic acid proteins. Interestingly, different proteome and glycoproteome profiles were observed between the two recombinant strains and the wild-type strain. We have shown here that the construction of the recombinant strains of M. microti has altered the proteome and glycosylation profiles of these strains, leading us to ask what impact these changes might have on the immune response.

Mutation on lysX from Mycobacterium avium hominissuis impacts the host-pathogen interaction and virulence phenotype

The lysX gene from Mycobacterium avium hominissuis (MAH) is not only involved in cationic antimicrobial resistance but also regulates metabolic activity. An MAH lysX deficient mutant was shown to exhibit a metabolic shift at the extracellular state preadapting the bacteria to the conditions inside host-cells. It further showed stronger growth in human monocytes. In the present study, the LysX activity on host-pathogen interactions were analyzed. The lysX mutant from MAH proved to be more sensitive toward host-mediated stresses such as reactive oxygen species. Further, the lysX mutant exhibited increased inflammatory response in PBMC and multinucleated giant cell (MGC) formation in human macrophages during infection studies. Coincidentally, the lysX mutant strain revealed to be more reproductive in the Galleria mellonella infection model. Together, these data demonstrate that LysX plays a role in regulating the bacillary load in host organisms and the lack of lysX gene facilitates MAH adaptation to intracellular host-habitat, thereby suggesting an essential role of LysX in the modulation of host-pathogen interaction.

O-Methylation of the Glycopeptidolipid Acyl Chain Defines Surface Hydrophobicity of Mycobacterium abscessus and Macrophage Invasion

Mycobacterium abscessus, an emerging pathogen responsible for severe lung infections in cystic fibrosis patients, displays either smooth (S) or rough (R) morphotypes. The S-to-R transition is associated with reduced levels of glycopeptidolipid (GPL) production and is correlated with increased pathogenicity in animal and human hosts. While the structure of GPL is well established, its biosynthetic pathway is incomplete. In addition, the biological functions of the distinct structural parts of this complex lipid remain elusive. Herein, the fmt gene encoding a putative O-methyltransferase was deleted in the M. abscessus S variant. Subsequent biochemical and structural analyses demonstrated that methoxylation of the fatty acyl chain of GPL was abrogated in the Δfmt mutant, and this defect was rescued upon complementation with a functional fmt gene. In contrast, the introduction of fmt derivatives mutated at residues essential for methyltransferase activity failed to complement GPL defects, indicating that fmt encodes an O-methyltransferase. Unexpectedly, phenotypic analyses showed that Δfmt was more hydrophilic than its parental progenitor, as demonstrated by hexadecane-aqueous buffer partitioning and atomic force microscopy experiments with hydrophobic probes. Importantly, the invasion rate of THP-1 macrophages by Δfmt was reduced by 50% when compared to the wild-type strain. Together, these results indicate that Fmt O-methylates the lipid moiety of GPL and plays a substantial role in conditioning the surface hydrophobicity of M. abscessus as well as in the early steps of the interaction between the bacilli and macrophages.

Lectin PLL3, a Novel Monomeric Member of the Seven-Bladed β-Propeller Lectin Family

The Photorhabdus species is a Gram-negative bacteria of the family Morganellaceae that is known for its mutualistic relationship with Heterorhabditis nematodes and pathogenicity toward insects. This study is focused on the characterization of the recombinant lectin PLL3 with an origin in P. laumondii subsp. laumondii. PLL3 belongs to the PLL family of lectins with a seven-bladed β-propeller fold. The binding properties of PLL3 were tested by hemagglutination assay, glycan array, isothermal titration calorimetry, and surface plasmon resonance, and its structure was determined by X-ray crystallography. Obtained data revealed that PLL3 binds similar carbohydrates to those that the other PLL family members bind, with some differences in the binding properties. PLL3 exhibited the highest affinity toward l-fucose and its derivatives but was also able to interact with O-methylated glycans and other ligands. Unlike the other members of this family, PLL3 was discovered to be a monomer, which might correspond to a weaker avidity effect compared to homologous lectins. Based on the similarity to the related lectins and their proposed biological function, PLL3 might accompany them during the interaction of P. laumondii with both the nematode partner and the insect host.

Experimental and theoretical study of the role of CH/π interactions in the aminolysis reaction of acetyl galactoside

Molecular recognition of saccharides is a growing field, which has many implications in cancer therapy, drug discovery, and cellular communication among others. The participation of CH/π interactions in this event is well known. Nevertheless, the intrinsic role of CH/π for modulating chemical reactions is still far from being applicable. In this experimental and computational work we have evaluated the participation of CH/π interactions in the aminolysis reaction of acetyl galactoside promoted with different 6-substituted 2(1H)-pyridones. Two features have been incorporated to the promoter molecular structure, on one end the promoting pyridone group and on the other end the recognition moiety, joined together by an alkyne spacer. The small increment in the observed pseudo-first-order rate constant values (k_obs) was related to the stability of the transition state provided by noncovalent interactions, including CH/π interactions. A longer alkyne spacer was necessary to improve the molecular recognition of the galactoside substrate. The trend of the calculated activation energy values (ΔE_RTS) was in good accordance with the experimental rate constant values.

Structural properties of D-mannopyranosyl rings containing O-acetyl side-chains

The crystal structures of 1,2,3,4,6-penta-O-acetyl-α-D-mannopyranose, C₁₆H₂₂O₁₁, and 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl-(1→2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl-(1→3)-1,2,4,6-tetra-O-acetyl-α-D-mannopyranose, C₄₀H₅₄O₂₇, were determined and compared to those of methyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside, methyl α-D-mannopyranoside and methyl α-D-mannopyranosyl-(1→2)-α-D-mannopyranoside to evaluate the effects of O-acetylation on bond lengths, bond angles and torsion angles. In general, O-acetylation exerts little effect on the exo- and endocyclic C-C and endocyclic C-O bond lengths, but the exocyclic C-O bonds involved in O-acetylation are lengthened by ∼0.02 Å. The conformation of the O-acetyl side-chains is highly conserved, with the carbonyl O atom either eclipsing the H atom attached to a 2°-alcoholic C atom or bisecting the H-C-H bond angle of a 1°-alcoholic C atom. Of the two C-O bonds that determine O-acetyl side-chain conformation, that involving the alcoholic C atom exhibits greater rotational variability than that involving the carbonyl C atom. These findings are in good agreement with recent solution NMR studies of O-acetyl side-chain conformations in saccharides. Experimental evidence was also obtained to confirm density functional theory (DFT) predictions of C-O and O-H bond-length behavior in a C-O-H fragment involved in hydrogen bonding.

Mycobacterium abscessus glycopeptidolipids inhibit macrophage apoptosis and bacterial spreading by targeting mitochondrial cyclophilin D

Mycobacterium abscessus (MAB) is a species of nontuberculous mycobacteria (NTM) and a major causative pathogen of pulmonary diseases especially in patients with cystic fibrosis. MAB infection is notoriously difficult to treat because of its intrinsic or inducible resistance to most antibiotics. The rough (R) morphotype of MAB, lacking cell surface glycopeptidolipids (GPLs), is associated with more severe and persistent infection than the smooth (S) type; however, the mechanisms underlying the R type's virulence and the relation with GPLs remain unclear. In this study, we found that R-type MAB is much more proapoptotic than the S type, as a result of GPL-mediated inhibition of macrophage apoptosis. Polar GPLs inhibited an apoptotic response (induced by proapoptotic stimuli) by suppressing ROS production and the cytochrome c release and by preserving mitochondrial transmembrane potential. Furthermore, GPLs were found to be targeted to mitochondria and interacted with cyclophilin D; their acetylation was essential for this interaction. Finally, GPLs inhibited the intracellular growth and bacterial spreading of R-type MAB among macrophages via apoptosis inhibition. These findings suggest that GPLs limit MAB virulence by inhibiting apoptosis and the spread of bacteria and therefore provide a novel insight into the mechanism underlying virulence of MAB.

O-Acetyl Side-Chains in Monosaccharides: Redundant NMR Spin-Couplings and Statistical Models for Acetate Ester Conformational Analysis

α- and β-d-glucopyranose monoacetates 1-3 were prepared with selective ¹³C enrichment in the O-acetyl side-chain, and ensembles of ¹³C-¹H and ¹³C-¹³C NMR spin-couplings (J-couplings) were measured involving the labeled carbons. Density functional theory (DFT) was applied to a set of model structures to determine which J-couplings are sensitive to rotation of the ester bond θ. Eight J-couplings (¹J_CC, ²J_CH, ²J_CC, ³J_CH, and ³J_CC) were found to be sensitive to θ, and four equations were parametrized to allow quantitative interpretations of experimental J-values. Inspection of J-coupling ensembles in 1-3 showed that O-acetyl side-chain conformation depends on molecular context, with flanking groups playing a dominant role in determining the properties of θ in solution. To quantify these effects, ensembles of J-couplings containing four values were used to determine the precision and accuracy of several 2-parameter statistical models of rotamer distributions across θ in 1-3. The statistical method used to generate these models has been encoded in a newly developed program, MA'AT, which is available for public use. These models were compared to O-acetyl side-chain behavior observed in a representative sample of crystal structures, and in molecular dynamics (MD) simulations of O-acetylated model structures. While the functional form of the model had little effect on the precision of the calculated mean of θ in 1-3, platykurtic models were found to give more precise estimates of the width of the distribution about the mean (expressed as circular standard deviations). Validation of these 2-parameter models to interpret ensembles of redundant J-couplings using the O-acetyl system as a test case enables future extension of the approach to other flexible elements in saccharides, such as glycosidic linkage conformation.

Inactivation of MSMEG_0412 gene drastically affects surface related properties of Mycobacterium smegmatis

Background

The outermost layer of mycobacterial cell wall is rich in lipids and glycolipids, surface molecules which differ among species. Mycobacterium smegmatis, an attractive model for the study of both pathogenic and non-pathogenic mycobacteria, presents glycopeptidolipids (GPLs). All the genes necessary for the biosynthesis of such molecules are clustered in a single region of 65 kb and among them, the msmeg_0412 gene has not been characterized yet. Here we report the isolation and subsequent analysis of a MSMEG_0412 null mutant strain.

Results

The inactivation of the msmeg_0412 gene had a drastic impact on bacterial surface properties which resulted in the lack of sliding motility, altered biofilm formation and enhanced drug susceptibility. The GPLs analysis showed that the observed mutant phenotype was due to GPLs deficiencies on the mycobacterial cell wall. In addition, we report that the expression of the gene is enhanced in the presence of lipidic substrates and that the encoded protein has a membrane localization.

Conclusion

msmeg_0412 plays a crucial role for GPLs production and translocation on M. smegmatis surface. Its deletion alters the surface properties and the antibiotic permeability of the mycobacterial cell barrier.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0888-z) contains supplementary material, which is available to authorized users.

High-throughput transcriptomics reveals common and strain-specific responses of human macrophages to infection with Mycobacterium abscessus Smooth and Rough variants

Background

Mycobacterium abscessus (MAB) is an emerging pathogen causing pulmonary infections in those with inflammatory lung disorders, such as Cystic Fibrosis (CF), and is associated with the highest fatality rate among rapidly growing mycobacteria (RGM). Phenotypically, MAB manifests as either a Smooth (MAB-S) or a Rough (MAB-R) morphotype, which differ in their levels of cell wall glycopeptidolipids (GPLs) and in their pathogenicity in vivo. As one of the primary immune cells encountered by MAB, we sought to examine the early transcriptional events within macrophages, following infection with both MAB-S or MAB-R.

Results

We sampled the transcriptomes (mRNA and miRNA) of THP-1-derived macrophages infected with both MAB-R and MAB-S at 1, 4 and 24 h post-infection (hpi) using RNA-seq. A core set of 606 genes showed consistent expression profiles in response to both morphotypes, corresponding to the early transcriptional response to MAB. The core response is type I Interferon (IFN)-driven, involving the NF-κB and MAPK signaling pathways with concomitant pro-inflammatory cytokine production, and network analysis identified STAT1, EGR1, and SRC as key hub and bottleneck genes. MAB-S elicited a more robust transcriptional response at both the mRNA and miRNA levels, which was reflected in higher cytokine levels in culture supernatants. The transcriptional profiles of macrophages infected with both morphotypes were highly correlated, however, and a direct comparison identified few genes to distinguish them. Most of the induced miRNAs have previously been associated with mycobacterial infection and overall miRNA expression patterns were similarly highly correlated between the morphotypes.

Conclusions

The report here details the first whole transcriptome analysis of the early macrophage response to MAB infection. The overall picture at the early stages of macrophage infection is similar to that of other mycobacteria, reflected in a core type I IFN and pro-inflammatory cytokine response. Large-scale transcriptional differences in the host response to the different MAB morphotypes are not evident in the early stages of infection, however the subset of genes with distinct expression profiles suggest potentially interesting differences in internal trafficking of MAB within macrophages.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2246-1) contains supplementary material, which is available to authorized users.

A GMC oxidoreductase homologue is required for acetylation of glycopeptidolipid in Mycobacterium smegmatis

The Mycobacterium tuberculosis Rv3409c gene is required for modulation of the Toll-like receptor 2 (TLR-2) signaling response in infected macrophages. Although each is annotated as encoding a cholesterol oxidase, neither Rv3409c nor its ortholog MSMEG1604 is required for the metabolism of cholesterol in mycobacteria. Here we report that a unique lipid, L1334, accumulates in a MSMEG1604 transposon mutant in the Mycobacterium smegmatis cell envelope. L1334 is a polar glycopeptidolipid that is hyperrhamnosylated and in which the 6-deoxytalose moiety is not acetylated. The alteration of L1334 acetylation is consistent with a reduced level of interference with TLR-2 signaling in mutant infected macrophages.

Innate defects of the IL-12/IFN-γ axis in susceptibility to infections by mycobacteria and salmonella

Since 1996, several studies characterizing the association between primary immunodeficiencies and susceptibility to infections with environmental and non-pathogenic mycobacteria such as the Bacillus Calmette-Guérin (Mycobacterium bovis Bacillus of Calmette Guérin strain) as well as disseminated infections by Salmonella spp. have been conducted. These conditions, grouped in the so-called Mendelian susceptibility to mycobacterial diseases, include a primary immunodeficiency caused by mutations in 7 autosomal genes (IFNGR1, IFNGR2, IL12B, IL12BR1, STAT1, ISG15, and IRF8) and an X-linked gene (NEMO). This syndrome presents a high degree of allelic heterogeneity and variable penetrance. This review focuses on the analysis of the first reported cases of these diseases, as well as on the molecular findings involved in each of them.

Structure and function of mycobacterium glycopeptidolipids from comparative genomics perspective

Glycopeptidolipids (GPLs) attached to the outer surface of the greasy cell envelope, are a class of important glycolipids synthesized by several non-tuberculosis mycobacteria. The deletion or structure change of GPLs confers several phenotypical changes including colony morphology, hydrophobicity, aggregation, sliding motility, and biofilm formation. In addition, GPLs, particular serovar specific GPLs, are important immunomodulators. This review aims to summarize the advance on the structure, function and biosynthesis of mycobacterium GPLs.

Methylation--an uncommon modification of glycans

A methyl (Me) group on a sugar residue is a rarely reported event. Until now, this type of modification has been found in the animal kingdom only in worms and molluscs, whereas it is more frequently present in some species of bacteria, fungi, algae and plants, but not in mammals. The monosaccharides involved as well as the positions of the Me groups on the sugar vary with species. Methylation appears to play a role in some recognition events, but details are still unknown. This review summarises the current knowledge on methylation of sugars in all types of organism.

Biochemical and biologic characterization of exosomes and microvesicles as facilitators of HIV-1 infection in macrophages

Exosomes and microvesicles (MV) are cell membranous sacs originating from multivesicular bodies and plasma membranes that facilitate long-distance intercellular communications. Their functional biology, however, remains incompletely understood. Macrophage exosomes and MV isolated by immunoaffinity and sucrose cushion centrifugation were characterized by morphologic, biochemical, and molecular assays. Lipidomic, proteomic, and cell biologic approaches uncovered novel processes by which exosomes and MV facilitate HIV-1 infection and dissemination. HIV-1 was "entrapped" in exosome aggregates. Robust HIV-1 replication followed infection with exosome-enhanced fractions isolated from infected cell supernatants. MV- and exosome-facilitated viral infections are affected by a range of cell surface receptors and adhesion proteins. HIV-1 containing exosomes readily completed its life cycle in human monocyte-derived macrophages but not in CD4(-) cells. The data support a significant role for exosomes as facilitators of viral infection.

Glycopeptidolipids: immuno-modulators in greasy mycobacterial cell envelope

Species of opportunistic mycobacteria are the major causative agent for disseminating pulmonary infections in immuno-compromised individuals. These naturally resistant strains recruit a unique type of glycolipid known as glycopeptidolipids (GPLs), noncovalently attached to the outer surface of their thick lipid rich cell envelope. Species specific GPLs constitute the chemical determinants of most nontuberculous mycobacterial serotypes, and their absence from the cell surface confers altered colony morphology, hydrophobicity, and inability to grow as biofilms. The objective of this review is to present a comprehensive account and highlight the renewed interest on this much neglected group of pleiotropic molecules with respect to their structural diversity and biosynthesis. In addition, the role of GPLs in mycobacterial survival, both intracellular and in the environment is also discussed. It also explores the possibility of identifying new targets for intervening Mycobacterium avium complex-related infections. These antigenic molecules have been considered to play a pivotal role in immune suppression and can also induce various cytokine mediated innate immune responses, the molecular mechanism of which remains obscure.

Structure and host recognition of serotype 13 glycopeptidolipid from Mycobacterium intracellulare

The Mycobacterium avium-M. intracellulare complex (MAIC) is divided into 28 serotypes by a species-specific glycopeptidolipid (GPL). Previously, we clarified the structures of serotype 7 GPL and two methyltransferase genes (orfA and orfB) in serotype 12 GPL. This study elucidated the chemical structure, biosynthesis gene, and host innate immune response of serotype 13 GPL. The oligosaccharide (OSE) structure of serotype 13 GPL was determined to be 4-2'-hydroxypropanoyl-amido-4,6-dideoxy-β-hexose-(1 → 3)-4-O-methyl-α-L-rhamnose-(1 → 3)-α-L-rhamnose-(1 → 3)-α-L-rhamnose-(1 → 2)-α-L-6-deoxy-talose by using chromatography, mass spectrometry, and nuclear magnetic resonance (NMR) analyses. The structure of the serotype 13 GPL was different from those of serotype 7 and 12 GPLs only in O-methylations. We found a relationship between the structure and biosynthesis gene cluster. M. intracellulare serotypes 12 and 13 have a 1.95-kb orfA-orfB gene responsible for 3-O-methylation at the terminal hexose, orfB, and 4-O-methylation at the rhamnose next to the terminal hexose, orfA. The serotype 13 orfB had a nonfunctional one-base missense mutation that modifies serotype 12 GPL to serotype 13 GPL. Moreover, the native serotype 13 GPL was multiacetylated and recognized via Toll-like receptor 2. The findings presented here imply that serotypes 7, 12, and 13 are phylogenetically related and confirm that acetylation of the GPL is necessary for host recognition. This study will promote better understanding of the structure-function relationships of GPLs and may open a new avenue for the prevention of MAIC infections.

Methyl 2-acetamido-2-deoxy-β-D-glucopyranoside dihydrate and methyl 2-formamido-2-deoxy-β-D-glucopyranoside

Methyl 2-acetamido-2-deoxy-β-D-glucopyranoside (β-GlcNAcOCH(3)), (I), crystallizes from water as a dihydrate, C(9)H(17)NO(6)·H(2)O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2-formamido-2-deoxy-β-D-glucopyranoside (β-GlcNFmOCH(3)), (II), C(8)H(15)NO(6), also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted (4)C(1) chair conformations. Values of φ for (IA) and (IB) indicate ring distortions towards B(C2,C5) and (C3,O5)B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N-acyl side chain. Distortion towards B(C2,C5) was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C-N bond is anti (C-H is approximately anti to N-H), although the conformation about the latter bond within this group varies by ~16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X-ray structures of (I) and (II) with those of other GlcNAc mono- and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state.

In situ TLR2 and TLR4 expression in a murine model of mycetoma caused by Nocardia brasiliensis

Actinomycetoma caused by Nocardia brasiliensis is a common disease in tropical regions. This ailment is characterized by a localized chronic inflammation that mainly affects the lower limbs. Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns, inducing the production of proinflammatory mediators. The role of TLRs in the immune response against N. brasiliensis is unknown. The aim of this work was to locate and quantify in a murine model the expression of TLR2 and TLR4 in the infection site using reverse transcription-PCR and immunohistochemistry. The results showed that TLR2 expression increased in the infected tissue, whereas TLR4 expression decreased. The presence of TLR2 and TLR4 was demonstrated in different cell populations throughout the chronic infectious process. In the early stages of this process, TLR2 was expressed in neutrophils and macrophages in direct contact with the inoculum, whereas TLR4 was observed in mast cells. In the advanced stages of the infection, TLR2 was expressed in foam cells and fibroblasts and was likely associated with bacterial containment, while TLR4 was downregulated, probably resulting in an imbalance between the host immune response and the bacterial load that favoured chronic disease.

Overexpression of proinflammatory TLR-2-signalling lipoproteins in hypervirulent mycobacterial variants

Changes in the cell envelope composition of mycobacteria cause major changes in cytokine profiles of infected antigen presenting cells. We describe here the modulation of inflammatory responses by Mycobacterium abscessus, an emerging pathogen in cystic fibrosis. M. abscessus is able to switch from a smooth (S) to a rough (R) morphotype by the loss of a surface glycopeptidolipid. R variants are associated with severe clinical forms and a 'hyper-proinflammatory' response in ex vivo and in vivo models. Using partitioning of cell surface components we found that a complex fraction, more abundant in R variants than in S variants, made a major contribution to the TLR-2-dependent hyper-proinflammatory response induced by R variants. Lipoproteins were the main TLR-2 agonists in this fraction, consistent with the larger amounts of 16 lipoproteins in cell surface extracts from R variants; 15 out of 16 being more strongly induced in R variant than in S variant. Genetic interruption of glycopeptidolipid pathway in wild-type S variant resulted in R phenotype with similar induction of lipoprotein genes. In conclusion, R morphotype in M. abscessus is associated with increased synthesis/exposure at the cell surface of lipoproteins, these changes profoundly modifying the innate immune response through TLR-2-dependent mechanisms.

Novel rhamnosyltransferase involved in biosynthesis of serovar 4-specific glycopeptidolipid from Mycobacterium avium complex

Glycopeptidolipids (GPLs) are one of the major glycolipid components present on the surface of Mycobacterium avium complex (MAC) that belong to opportunistic pathogens distributed in the natural environment. The serovars of MAC, up to around 30 types, are defined by the variable oligosaccharide portions of the GPLs. Epidemiological studies show that serovar 4 is the most prevalent type, and the prognosis of pulmonary disease caused by serovar 4 is significantly worse than that caused by other serovars. However, little is known about the biosynthesis of serovar 4-specific GPL, particularly the formation of the oligosaccharide portion that determines the properties of serovar 4. To investigate the biosynthesis of serovar 4-specific GPL, we focused on one segment that included functionally unknown genes in the GPL biosynthetic gene cluster of a serovar 4 strain. In this segment, a putative hemolytic protein gene, hlpA, and its downstream gene were found to be responsible for the formation of the 4-O-methyl-rhamnose residue, which is unique to serovar 4-specific GPL. Moreover, functional characterization of the hlpA gene revealed that it encodes a rhamnosyltransferase that transfers a rhamnose residue via 1→4 linkage to a fucose residue of serovar 2-specific GPL, which is a key pathway leading to the synthesis of oligosaccharide of serovar 4-specific GPL. These findings may provide clues to understanding the biological role of serovar 4-specific GPL in MAC pathogenicity and may also provide new insights into glycosyltransferase, which generates structural and functional diversity of GPLs.

Mannose receptor-dependent delay in phagosome maturation by Mycobacterium avium glycopeptidolipids

The ability of pathogenic mycobacteria to block phagosome-lysosome fusion is critical for its pathogenesis. The molecules expressed by mycobacteria that inhibit phagosome maturation and the mechanism of this inhibition have been extensively studied. Recent work has indicated that mannosylated lipoarabinomannan (ManLAM) isolated from Mycobacterium tuberculosis can function to delay phagosome-lysosome fusion and that this delay requires the interaction of ManLAM with the mannose receptor (MR). However, the molecules expressed by other pathogenic mycobacteria that function to inhibit phagosome maturation have not been well described. In the present study, we show that phagosomes containing silica beads coated with glycopeptidolipids (GPLs), a major surface component of Mycobacterium avium, showed limited acidification and delayed recruitment of late endosomal/lysosomal markers compared to those of phosphatidylcholine-coated beads. The carbohydrate component of the GPLs was required, as beads coated only with the lipopeptide core failed to delay phagosome-lysosome fusion. Moreover, the ability of GPLs to delay phagosome maturation was dependent on the macrophage expression of the MR. Using CHO cells expressing the MR, we confirmed that the GPLs bind this receptor. Finally, human monocyte-derived macrophages knocked down for MR expression showed increased M. avium phagosome-lysosome fusion relative to control cells. Together, the data indicate that GPLs can function to delay phagosome-lysosome fusion and suggest that GPLs, like ManLAM, work through the MR to mediate this activity.