Roles of N-linked glycans in the recognition of microbial lipopeptides and lipoproteins by TLR2

Revisiting the immunopathology of congenital disorders of glycosylation: an updated review

Glycosylation is a critical post-translational modification that plays a pivotal role in several biological processes, such as the immune response. Alterations in glycosylation can modulate the course of various pathologies, such as the case of congenital disorders of glycosylation (CDG), a group of more than 160 rare and complex genetic diseases. Although the link between glycosylation and immune dysfunction has already been recognized, the immune involvement in most CDG remains largely unexplored and poorly understood. In this study, we provide an update on the immune dysfunction and clinical manifestations of the 12 CDG with major immune involvement, organized into 6 categories of inborn errors of immunity according to the International Union of Immunological Societies (IUIS). The immune involvement in phosphomannomutase 2 (PMM2)-CDG - the most frequent CDG - was comprehensively reviewed, highlighting a higher prevalence of immune issues during infancy and childhood and in R141H-bearing genotypes. Finally, using PMM2-CDG as a model, we point to links between abnormal glycosylation patterns in host cells and possibly favored interactions with microorganisms that may explain the higher susceptibility to infection. Further characterizing immunopathology and unusual host-pathogen adhesion in CDG can not only improve immunological standards of care but also pave the way for innovative preventive measures and targeted glycan-based therapies that may improve quality of life for people living with CDG.

The evolving role of methanogenic archaea in mammalian microbiomes

Methanogenic archaea (methanogens) represent a diverse group of microorganisms that inhabit various environmental and host-associated microbiomes. These organisms play an essential role in global carbon cycling given their ability to produce methane, a potent greenhouse gas, as a by-product of their energy production. Recent advances in culture-independent and -dependent studies have highlighted an increased prevalence of methanogens in the host-associated microbiome of diverse animal species. Moreover, there is increasing evidence that methanogens, and/or the methane they produce, may play a substantial role in human health and disease. This review addresses the expanding host-range and the emerging view of host-specific adaptations in methanogen biology and ecology, and the implications for host health and disease.

Mycobacterium bovis BCG infection alters the macrophage N-glycome

Macrophage glycosylation is essential to initiate the host-immune defense but may also be targeted by pathogens to promote infection. Indeed, the alteration of the cell-surface glycosylation status may affect the binding of lectins involved in cell activation and adhesion. Herein, we demonstrate that infection by M. bovis BCG induces the remodeling of the N-glycomes of both human primary blood monocyte-derived macrophages (MDM) and macrophage-cell line THP1. MALDI-MS based N-glycomic analysis established that mycobacterial infection induced increased synthesis of biantennary and multifucosylated complex type N-glycans. In contrast, infection of macrophages by M. bovis BCG did not modify the glycosphingolipids composition of macrophages. Further nano-LC-MSⁿ glycotope-centric analysis of total N-glycans demonstrated that the increased fucosylation was due to an increased expression of the Le^x (Galβ1-4[Fucα1-3]GlcNAc) epitope, also known as stage-specific embryonic antigen-1. Modification of the surface expression of Le^x was further confirmed in both MDM and THP-1 cells by FACS analysis using an α1,3-linked fucose specific lectin. Activation with the mycobacterial lipopeptide Pam3Lp19, an agonist of toll-like receptor 2, did not modify the overall fucosylation pattern, which suggests that the infection process is required to modify surface glycosylation. These results pave the way toward the understanding of infection-triggered cell-surface remodeling of macrophages.

The direct and indirect effects of glycans on immune function

The biological impact of glycans is as diverse and complex as the impact of proteins on biology. Familiar roles include those as a protein folding checkpoint in the endoplasmic reticulum and as a modulator of the serum half-life of secreted glycoproteins, but it has become clear over the last several decades that glycans are key signaling moieties, participate in cell-cell interactions and modulate the function of individual proteins, to name but a few examples. In the immune system, the majority of microbial "patterns" are glycans or glycoconjugates, while virtually all cell surface receptors are glycoproteins, and antibody glycosylation critically influences antibody function. In order to provide a simple contextual framework to understand the myriad roles, glycans play in immunity, we propose that glycan effects are considered direct or indirect, depending on their direct participation or their indirect effects on other components in a given biological process or pathway. Here, we present the published evidence that supports this framework, which ultimately leads to the conclusion that we should learn to embrace the complexity inherent to the glycome and its potential as a largely uncharted but target rich area of new therapeutic investigation.

Activation of NLRP3 inflammasome in macrophages by mycoplasmal lipoproteins and lipopeptides

The NLRP3 inflammasome, an intracellular sensor consisting of the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3), the adaptor protein apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC), and procaspase-1, plays critical roles in host defense against microbial pathogens by inducing production of interleukin-1β (IL-1β) and IL-18. Mycoplasma salivarium and Mycoplasma pneumoniae cells activated murine bone marrow-derived macrophages (BMMs) to induce production of IL-1α, IL-1β, and IL-18. The IL-1β production-inducing activities of these mycoplasmas toward BMMs from Toll-like receptor 2 (TLR2)-deficient mice were significantly attenuated compared with those from C57BL/6 mice (B6BMMs). This result suggests the possibility that their lipoproteins as TLR2 agonists are involved in the activity. Lipoproteins of M. salivarium and M. pneumoniae (MsLP and MpLP), and the M. salivarium-derived lipopeptide FSL-1 induced IL-1β production by B6BMMs, but not by BMMs from caspase-1-, NLRP3- or ASC-deficient mice. The activities of MsLP and MpLP were not downregulated by the proteinase K treatment, suggesting that the active sites are their N-terminal lipopeptide moieties. B6BMMs internalized the mycoplasmal N-terminal lipopeptide FSL-1 at least 30 min after incubation, FSL-1-containing endosomes started to fuse with the lysosomes around 2 hours, and then FSL-1 translocated into the cytosol from LAMP-1⁺ endosomes. The artificial delivery of FSL-1 into the cytosol of B6BMMs drastically enhanced the IL-1β production-inducing activity. FSL-1 as well as the representative NLRP3 inflammasome activator nigericin induced the NLRP3/ASC speck, but FSL-1 located in a compartment different from the NLRP3/ASC speck.

Modulation of functional characteristics of resident and thioglycollate-elicited peritoneal murine macrophages by a recombinant banana lectin

We demonstrated that a recombinant banana lectin (rBanLec), which structural characteristics and physiological impacts highly resemble those reported for its natural counterparts, binds murine peritoneal macrophages and specifically modulates their functional characteristics. By using rBanLec in concentrations ranging from 1 μg to 10 μg to stimulate resident (RMs) and thioglycollate-elicited (TGMs) peritoneal macrophages from BALB/c and C57BL/6 mice, we have shown that effects of rBanLec stimulation depend on its concentration but also on the functional status of macrophages and their genetic background. rBanLec, in a positive dose-dependent manner, promotes the proliferation of TGMs from both BALB/c and C57BL/6 mice, while its mitogenic influence on RMs is significantly lower (BALB/c mice) or not detectable (C57BL/6 mice). In all peritoneal macrophages, irrespective of their type and genetic background, rBanLec, in a positive dose dependent manner, enhances the secretion of IL-10. rBanLec stimulation of RMs from both BALB/c and C57BL/6 resulted in a positive dose-dependent promotion of proinflammatory phenotype (enhancement of NO production and IL-12 and TNFα secretion, reduction of arginase activity). Positive dose-dependent skewing toward proinflammatory phenotype was also observed in TGMs from C57BL/6 mice. However, the enhancement of rBanLec stimulation promotes skewing of TGMs from BALB/c mice towards anti-inflammatory profile (reduction of NO production and IL-12 secretion, enhancement of arginase activity and TGFβ and IL-4 secretion). Moreover, we established that rBanLec binds oligosaccharide structures of TLR2 and CD14 and that blocking of signaling via these receptors significantly impairs the production of TNFα and NO in BALB/c macrophages. Since the outcome of rBanLec stimulation depends on rBanLec concentration as well as on the functional characteristics of its target cells and their genetic background, further studies are needed to investigate its effects under physiological and specific pathological conditions.

Molecular characterization and expression of a novel Toll gene from the swimming crab Portunus trituberculatus

Tolls/Toll-like receptors (TLRs) are important cell-surface receptors serving as pattern recognition receptors (PRRs) in the Tolls/TLRs signaling pathway of innate immune responses. In the present study, we isolated and characterized a novel Toll gene (PtToll) from Portunus trituberculatus, and further investigated its expression in various tissues of crab hosts challenged with the parasitic dinoflagellate Hematodinium. The full-length cDNA of PtToll was 3745 bp, with a 3012 bp open reading frame (ORF) encoding 1003 amino acids. Conserved domains consist of 15 tandem leucine-rich repeats (LRRs), a single-pass transmembrane segment (TM) and a cytoplasmic Toll/interleukin-1R (TIR) domain. The PtToll protein shared high similarity to other crustacean Tolls and was clustered with the crustacean Tolls in the phylogenetic tree. The PtToll gene was constitutively expressed in various tissues of P. trituberculatus, with the highest expression in hemocytes. After being challenged with the parasite, the transcripts of PtToll reacted immediately with significant alterations in all the tested tissues, and decreased consistently in most of the detected tissues (e.g., hemocytes, gill, heart, and muscle) within 24h. Then the transcripts of PtToll were significantly up-regulated in hemocytes and heart at 48 h, and in hepatopancreas at 48 and 96 h post the parasitic challenge. By 192 h post challenge, the transcriptional level of PtToll indicated a significant suppression or a decreasing trend. The fluctuations of PtToll gene expression suggested that PtToll was closely associated with intrusion of the Hematodinium parasites, and may possess a vital and systematic function in the innate immunity of P. trituberculatus against the parasitic infection.

Recognition of TLR2 N-glycans: critical role in ArtinM immunomodulatory activity

TLR2 plays a critical role in the protection against Paracoccidioides brasiliensis conferred by ArtinM administration. ArtinM, a D-mannose-binding lectin from Artocarpus heterophyllus, induces IL-12 production in macrophages and dendritic cells, which accounts for the T helper1 immunity that results from ArtinM administration. We examined the direct interaction of ArtinM with TLR2using HEK293A cells transfected with TLR2, alone or in combination with TLR1 or TLR6, together with accessory proteins. Stimulation with ArtinM induced NF-κB activation and interleukin (IL)-8 production in cells transfected with TLR2, TLR2/1, or TLR2/6. Murine macrophages that were stimulated with ArtinM had augmented TLR2 mRNA expression. Furthermore, pre-incubation of unstimulated macrophages with an anti-TLR2 antibody reduced the cell labeling with ArtinM. In addition, a microplate assay revealed that ArtinM bound to TLR2 molecules that had been captured by specific antibodies from a macrophages lysate. Notably,ArtinM binding to TLR2 was selectively inhibited when the lectin was pre-incubated with mannotriose. The biological relevance of the direct interaction of ArtinM with TLR2 glycans was assessed using macrophages from TLR2-KOmice, which produced significantly lower levels of IL-12 and IL-10 in response to ArtinM than macrophages from wild-type mice. Pre-treatment of murine macrophages with pharmacological inhibitors of signaling molecules demonstrated the involvement of p38 MAPK and JNK in the IL-12 production induced by ArtinM and the involvement ofPI3K in IL-10 production. Thus, ArtinM interacts directly with TLR2 or TLR2 heterodimers in a carbohydrate recognition-dependent manner and functions as a TLR2 agonist with immunomodulatory properties.

The immunomodulatory effect of plant lectins: a review with emphasis on ArtinM properties

Advances in the glycobiology and immunology fields have provided many insights into the role of carbohydrate-protein interactions in the immune system. We aim to present a comprehensive review of the effects that some plant lectins exert as immunomodulatory agents, showing that they are able to positively modify the immune response to certain pathological conditions, such as cancer and infections. The present review comprises four main themes: (1) an overview of plant lectins that exert immunomodulatory effects and the mechanisms accounting for these activities; (2) general characteristics of the immunomodulatory lectin ArtinM from the seeds of Artocarpus heterophyllus; (3) activation of innate immunity cells by ArtinM and consequent induction of Th1 immunity; (4) resistance conferred by ArtinM administration in infections with intracellular pathogens, such as Leishmania (Leishmania) major, Leishmania (Leishmania) amazonensis, and Paracoccidioides brasiliensis. We believe that this review will be a valuable resource for more studies in this relatively neglected area of research, which has the potential to reveal carbohydrate targets for novel prophylactic and therapeutic strategies.

Milk matters: soluble Toll-like receptor 2 (sTLR2) in breast milk significantly inhibits HIV-1 infection and inflammation

The majority of infants who breastfeed from their HIV-positive mothers remain uninfected despite constant and repeated exposure to virus over weeks to years. This phenomenon is not fully understood but has been closely linked to innate factors in breast milk (BM). Most recently we have focused on one such innate factor, soluble Toll-like receptor 2 (sTLR2) for its significant contribution as an inhibitor of inflammation triggered by bacterial and viral antigens. We hypothesized that sTLR2 in BM inhibits immune activation/inflammation and HIV-1 infection. sTLR2 protein profiles were analyzed in HIV-uninfected BM and showed dramatic variability in expression concentration and predominant sTLR2 forms between women. sTLR2 immunodepleted BM, versus mock-depleted BM, incubated with Pam₃CSK₄ lead to significant increases in IL-8 production in a TLR2-dependant fashion in U937, HEK293-TLR2, and Caco-2. Importantly, TLR2-specific polyclonal and monoclonal antibody addition to BM prior to cell-free R5 HIV-1 addition led to significantly (P<0.01, P<0.001, respectively) increased HIV-1 infection in TZM-bl reporter cells. To confirm these findings, sTLR2-depletion in BM led to significantly (P<0.001) increased HIV-1 infection in TZM-bl cells. Notably, immunodepletion does not allow for the complete removal of sTLR2 from BM, thus functional testing shown here may underestimate the total effect elicited by sTLR2 against HIV-1 and synthetic bacterial ligand. This study provides evidence for the first time that sTLR2 in BM may provide a dual protective role for infants breastfeeding from their HIV-infected mothers by; (1) immunomodulating pro-inflammatory responses to bacterial ligands, and (2) directly inhibiting cell-free HIV-1 infection. Thus, sTLR2 in BM may be critical to infant health and prove beneficial in decreasing vertical HIV-1 transmission to infants.

ArtinM offers new perspectives in the development of antifungal therapy

The thermally dimorphic fungus Paracoccidioides brasiliensis is the causative agent of paracoccidioidomycosis (PCM), the most frequent systemic mycosis that affects the rural populations in Latin America. Despite significant developments in antifungal chemotherapy, its efficacy remains limited since drug therapy is prolonged and associated with toxic side effects and relapses. In response to these challenges, it is now recognized that several aspects of antifungal immunity can be modulated to better deal with fungal infections. A common idea for halting fungal infections has been the need to activate a cell-based, pro-inflammatory Th1 immune response to improve the fungal elimination. ArtinM, a D-mannose binding lectin from Artocarpus heterophyllus, has the property of modulating immunity against several intracellular pathogens. Here, we review the immunomodulatory activity of ArtinM during experimental PCM in mice. Both prophylactic and therapeutic protocols of ArtinM administration promotes a Th1 immune response balanced by IL-10, which outstandingly reduces the fungal load in organs of the treated mice while maintaining a controlled inflammation at the site of infection. A carbohydrate recognition-based interaction of ArtinM with Toll-like receptor 2 (TLR2) accounts for initiating the immunomodulatory effect of the lectin. The precise identification of the TLR2 N-glycan(s) targeted by ArtinM may support novel basis for the development of antifungal therapy.

A Crassostrea gigas Toll-like receptor and comparative analysis of TLR pathway in invertebrates

Toll-like receptor (TLR) signaling pathway was an important and evolutionarily conserved innate immune pathway. Evolutionary lineage of this pathway in the Lophotrochozoans is still less understood. In this study, we cloned a novel TLR, a key component of TLR pathway, from Crassostrea gigas, and named it CgToll-1. The 4343 base pairs full-length cDNA was assembled with the 3' and 5' RACE (rapid amplification of cDNA ends) PCR results, and containing a 3540 bp open reading frame, which encoding a putative TLR protein of 1179 amino acid residues. Real-time reverse transcription polymerase chain reaction analysis revealed that the highest CgToll-1 expression level was in hemolymph, and the expression pattern in hemolymph dramatically increased in the presence of bacteria Vibrio anguillarum. Furthermore, TLR pathway core genes of mollusks were searched and compared with model invertebrates. Phylogenetic trees of two downstream genes (IκB, Rel) showed that mollusks genes were closer to Drosophila melanogaster than Strongylocentrotus purpuratus, while three upstream genes (MyD88, IRAK, TRAF6) showed the opposite propensity. We have also detected that these two downstream genes were significantly more conservative than the three upstream genes based on amino acid sequence alignment. We found no significant difference between the codon usage biases of TLR pathway genes. This study suggests that CgToll-1 was a constitutive and inducible protein and thus could play an important role in the immune responses against bacterium infection. Besides, comparative analysis of TLR pathway showed that gene loss and divergence might exist during evolution in invertebrate.

Carbon monoxide suppresses membrane expression of TLR4 via myeloid differentiation factor-2 in betaTC3 cells

Islet allografts from donor mice exposed to CO are protected from immune rejection after transplantation via the suppression of membrane trafficking/activation of TLR4 in islets/beta cells. The molecular mechanisms of how CO suppresses TLR4 activation in beta cells remain unclear and are the focus of this study. Cells of the insulinoma cell line, betaTC3, were stably transfected with pcDNA3-TLR4-YFP and pDsRed-Monomer-Golgi plasmids and used to identify the subcellular distribution of TLR4 before and after LPS stimulation by confocal microscopy. Immunofluorescence analysis revealed that TLR4 mainly resides in the Golgi apparatus in betaTC3 cells when in a quiescent state. LPS stimulation led to a rapid trafficking of TLR4 from the Golgi to the cell membrane. Physical interaction between TLR4 and myeloid differentiation factor-2 (MD-2) was confirmed by immunoprecipitation. Depleting MD-2 using small interfering RNA or blocking the N-glycosylation of cells using tunicamycin blocked membrane trafficking of TLR4. Pre-exposing cells to CO at a concentration of 250 parts per million suppressed membrane trafficking of TLR4 via inhibiting its glycosylation and the interaction between TLR4 and MD-2. In conclusion, MD-2 is required for the glycosylation of TLR4 and its consequent membrane trafficking in betaTC3 cells. CO suppresses membrane activation of TLR4 via blocking its glycosylation and the physical interaction between TLR4 and MD-2.

CD14+ monocytes are vulnerable and functionally impaired under endoplasmic reticulum stress in patients with type 2 diabetes

OBJECTIVE

Although patients with diabetes suffer from increased infections and a higher incidence of cancer due to impaired immune function, details on diabetes-induced decrease in immunity are lacking. We assessed how immune-mediating peripheral blood mononuclear cells (PBMCs) are affected in diabetes.

RESEARCH DESIGN AND METHODS

From 33 patients with type 2 diabetes and 28 healthy volunteers, we obtained PBMCs and investigated their susceptibility to apoptosis and functional alteration.

RESULTS

In a subpopulation of PBMCs, monocytes derived from patients with diabetes were more susceptible to apoptosis than monocytes from healthy volunteers. Monocytes from patients with diabetes had decreased phagocytotic activity and were less responsive to Toll-like receptor (TLR) ligands, although the expression of TLRs did not differ significantly between the two groups. Furthermore, monocytes from patients with diabetes had a distinctly different gene expression profile compared with monocytes from normal volunteers as assessed with DNA microarray analysis. Specifically, quantitative real-time detection PCR measurements showed an elevated expression of the markers of endoplasmic reticulum (ER) stress in diabetic monocytes, and electron microscopic examination of monocytes revealed morphologic alterations in the ER of cells derived from patients with diabetes. Consistently, the ER stress inducer tunicamycin increased apoptosis of otherwise healthy monocytes and attenuated the proinflammatory responses to TLR ligands.

CONCLUSIONS

These data suggest that monocytes comprise a substantially impaired subpopulation of PBMCs in patients with diabetes and that ER stress is involved in these pathologic changes mechanistically. This implies that the affected monocytes should be investigated further to better understand diabetic immunity.

The Toll-like receptor 2 (TLR2) ligand FSL-1 is internalized via the clathrin-dependent endocytic pathway triggered by CD14 and CD36 but not by TLR2

Little is known of how Toll-like receptor (TLR) ligands are processed after recognition by TLRs. This study was therefore designed to investigate how the TLR2 ligand FSL-1 is processed in macrophages after recognition by TLR2. FSL-1 was internalized into the murine macrophage cell line, RAW264.7. Both chlorpromazine and methyl-beta-cyclodextrin, which inhibit clathrin-dependent endocytosis, reduced FSL-1 uptake by RAW264.7 cells in a dose-dependent manner but nystatin, which inhibits caveolae- and lipid raft-dependent endocytosis, did not. FSL-1 was co-localized with clathrin but not with TLR2 in the cytosol of RAW264.7 cells. These results suggest that internalization of FSL-1 is clathrin dependent. In addition, FSL-1 was internalized by peritoneal macrophages from TLR2-deficient mice. FSL-1 was internalized by human embryonic kidney 293 cells transfected with CD14 or CD36 but not by the non-transfected cells. Also, knockdown of CD14 or CD36 in the transfectants reduced FSL-1 uptake. In this study, we suggest that (i) FSL-1 is internalized into macrophages via a clathrin-dependent endocytic pathway, (ii) the FSL-1 uptake by macrophages occurs irrespective of the presence of TLR2, and (iii) CD14 and CD36 are responsible for the internalization of FSL-1.

Immunological analysis and pathological examination of gnotobiotic mice monoassociated with Mycoplasma pneumoniae

Although mycoplasmal pneumonia has been generally considered to be a disease with good prognosis, a pathogenic host immune response has been associated with its occurrence. In the present study, the pathogenic significance of the immune response was examined using germ-free mice either infected intranasally with Mycoplasma pneumoniae or inoculated with M. pneumoniae antigens (soluble antigen and partially purified antigen). In gnotobiotic mice monoassociated with M. pneumoniae, 10(4) c.f.u. M. pneumoniae per lung were isolated 2-28 days after infection. Inflammatory changes with infiltration of lymphocytes were histopathologically detected in the perivascular area at 2 and 7 days after infection. In the mice intranasally inoculated with soluble antigen or partially purified antigens (F6 and F10 antigens), infiltration of neutrophils and lymphocytes was histopathologically detected at 2 days after inoculation. Severe pneumonia with tissue destruction was observed in the mice inoculated with F6 antigen. A gamma interferon (IFN-gamma) dominant response in endogenous cytokine expression was observed in all the treated mice. These results indicate that inflammatory changes in the lung tissue were prolonged in gnotobiotic mice monoassociated with M. pneumoniae compared with mice inoculated with M. pneumoniae antigen. In addition, it was shown that IFN-gamma plays an important role in the pathogenesis of pneumonia in mice either infected with M. pneumoniae or inoculated with its antigen. In particular, the F6 antigen has been considered to be an important virulence factor in terms of induction of tissue injury causing infiltration of lymphocytes and neutrophils in the lung, suggesting a close interaction between the immune response and the occurrence of M. pneumoniae pneumonia.

Therapeutic administration of KM+ lectin protects mice against Paracoccidioides brasiliensis infection via interleukin-12 production in a toll-like receptor 2-dependent mechanism

KM(+) is a mannose-binding lectin from Artocarpus integrifolia that induces interleukin (IL)-12 production by macrophages and protective T helper 1 immune response against Leishmania major infection. In this study, we performed experiments to evaluate the therapeutic activity of jackfruit KM(+) (jfKM(+)) and its recombinant counterpart (rKM(+)) in experimental paracoccidioidomycosis. To this end, jfKM(+) or rKM(+) was administered to BALB/c mice 10 days after infection with Paracoccidiodes brasiliensis. Thirty days postinfection, lungs from the KM(+)-treated mice contained significantly fewer colony-forming units and little to no organized granulomas compared to the controls. In addition, lung homogenates from the KM(+)-treated mice presented higher levels of nitric oxide, IL-12, interferon-gamma, and tumor necrosis factor-alpha, whereas higher levels of IL-4 and IL-10 were detected in the control group. With mice deficient in IL-12, Toll-like receptor (TLR) 2, TLR4, or TLR adaptor molecule MyD88, we demonstrated that KM(+) led to protection against P. brasiliensis infection through IL-12 production, which was dependent on TLR2. These results demonstrated a beneficial effect of KM(+) on the severity of P. brasiliensis infection and may expand its potential use as a novel immunotherapeutic molecule.

N-Glycosylation of the Drosophila neural protein Chaoptin is essential for its stability, cell surface transport and adhesive activity

Glycosylation of proteins can modulate their function in a striking variety of systems, including immune responses, neuronal activities and development. The Drosophila protein, Chaoptin (Chp), is essential for the development and maintenance of photoreceptor cells. This protein is heavily glycosylated, but the possible role of this glycosylation is not well-understood. Here we show that mutations introduced into about 1/3 of 16 potential N-linked glycosylation sites within Chp impaired its cell adhesive activities when expressed in Drosophila S2 cells. Mutation of 2/3 of the glycosylation sites resulted in a marked decrease in Chp protein abundance. These results suggest that N-linked glycosylation of Chp is essential for its stability and activity.

Molecular characterization of toll-like receptor 2 of ruminants and comparative expression in nilgai (Boselaphus tragocamelus) vs. buffalo (Bubalus bubalis)

Toll-like receptors play role in the innate immune responses and orchestrate the adaptive immunity by induction of proinflammatory cytokines and up-regulation of costimulatory molecules. The present study has characterized TLR2 cDNA in nilgai, buffalo, sheep and goat that recognizes the peptidoglycan of Gram-positive bacteria. TLR2 coding sequences were amplified from monocytes cDNA and cloned in pGEMT-easy vector for nucleotide sequencing. Sequence analysis revealed 2355-bp-long TLR2 open reading frame encoding 784 amino acids in all the species studied. Nilgai TLR2 has 97.8% to 95.1% identity at nucleotide level and 96.2% to 92.7% identity at amino acid level with other ruminant species studied. Nonsynonymous substitutions exceeding synonymous substitutions indicated evolution of this receptor through positive selection among ruminants. Furthermore, basal TLR2 messenger RNA expression in different immune cells and tissues quantified by real-time polymerase chain reaction revealed highest level in in vitro derived dendritic cells followed by peripheral blood mononuclear cells. Skin and testes also expressed significant level in both nilgai and buffalo. Comparatively, nilgai immune cells and tissues expressed more TLR2 transcript than buffalo, thus elucidating stronger armamentarium of antibacterial immunity in nilgai as compared to buffalo.

Characterization and investigation of single nucleotide polymorphisms and a novel TLR2 mutation in the human TLR2 gene

In the innate immune system, TLR2 plays a central role for the response to a wide variety of microbial and endogenous danger signals. A considerable number of genetic polymorphisms within the human TLR2 gene have been reported in non-coding and coding sequences. Except for the Arg753Gln variant, however, their clinical relevance is unclear and the assessment of the effects of amino acid substitutions on receptor function is lacking. In the present study, we have characterized all known single nucleotide polymorphisms (SNPs) of TLR2 for their functional relevance in transiently transfected HEK293 cells subsequently exposed to a specific stimulus. Among the known non-synonymous SNPs in the TLR2 coding sequence, four SNPs (Thr411Ile, Tyr715stop, Tyr715Lys and Arg753Gln) were found to be functionally relevant in our experimental setting. In addition, we identified a new mutation Arg447stop leading to a premature stop codon in the extracellular portion of the receptor. TLR2-specific stimulation of whole blood from two heterozygote donors of this mutation resulted in a reduced secretion of pro-inflammatory cytokines. Finally, we tested the prevalence of these functional genetic variants in 169 healthy individuals of Caucasian origin for the mutations in the extracellular domain and 106 individuals for the mutations in the intracellular domain of the receptor. Except for 10 heterozygote donors of the Arg753Gln variant determined to be prevalent in 9.4% of the tested individuals, none of the other SNPs was found in this population.

Physicochemical and biological analysis of synthetic bacterial lipopeptides: validity of the concept of endotoxic conformation

The importance of the biological function and activity of lipoproteins from the outer or cytoplasmic membranes of Gram-positive and Gram-negative bacteria is being increasingly recognized. It is well established that they are like the endotoxins (lipopolysaccharide (LPS)), which are the main amphiphilic components of the outer membrane of Gram-negative bacteria, potent stimulants of the human innate immune system, and elicit a variety of proinflammatory immune responses. Investigations of synthetic lipopeptides corresponding to N-terminal partial structures of bacterial lipoproteins defined the chemical prerequisites for their biological activity and in particular the number and length of acyl chains and sequence of the peptide part. Here we present experimental data on the biophysical mechanisms underlying lipopeptide bioactivity. Investigation of selected synthetic diacylated and triacylated lipopeptides revealed that the geometry of these molecules (i.e. the molecular conformations and supramolecular aggregate structures) and the preference for membrane intercalation provide an explanation for the biological activities of the different lipopeptides. This refers in particular to the agonistic or antagonistic activity (i.e. their ability to induce cytokines in mononuclear cells or to block this activity, respectively). Biological activity of lipopeptides was hardly affected by the LPS-neutralizing antibiotic polymyxin B, and the biophysical interaction characteristics were found to be in sharp contrast to that of LPS with polymyxin B. The analytical data show that our concept of "endotoxic conformation," originally developed for LPS, can be applied also to the investigated lipopeptide and suggest that the molecular mechanisms of cell activation by amphiphilic molecules are governed by a general principle.