| 1. |
- Achour, Adnane
(författare)
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Structural studies of MHC class 1 complexes : implications for NK- and T-cell recognition
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cell-cell recognition events and the functional characteristics of the cell surface receptors that govern the responses of NK- and T-cells are central to molecular immunology. This thesis addresses the structural basis of such molecular recognition, more specifically the interaction between peptides and MHC class I molecules, as well as the interaction between such complexes and the inhibitory Ly49 receptors of NK cells or triggering antigen specific receptors of T-cells (TCR). A better understanding of the details of these receptor-ligand interactions may help us to develop tools to activate or inhibit specific NK- and T-cell subsets. The structure of MHC class I H-2Dd in complex with the HIV-derived peptide PI 8-110 was determined by X-ray crystallography at 2.4Å resolution following cloning, expression and refolding of bacterially expressed, non-glycosylated soluble MHC-peptide complexes. The cleft architecture displayed different structural features from that of other mouse MHC class I molecules, explaining the unusual peptide-binding motif. Comparative analysis of the H-2Dd structure and the previously published H-2Db structure was used to predict recognition motifs for the Ly49A receptor of NK cells. The structure was also used to interpret earlier studies of H-2Dd restricted cytotoxic T-cells. Specificity of the interaction of Ly49 NK cell receptors and their ligands was investigated using fluorescent tetrameric recombinant MHC-peptide complexes. These studies indicated that MHC class I associated glycan was not required for Ly49A-H-2Dd interaction, and that H-2Kb tetramer binding to Ly49C receptors was strongly influenced by the peptide presented by the class I molecule. Additionally, tetramer binding allowed visualization of receptor interactions previously undetected in functional studies, such as the binding of H-2Db to Ly49A and Ly49C, indicating the usefulness of this technology in dissecting molecular recognition events. The MHC class I tetramer technology was further used to investigate structural consequences of exchange of the mouse [beta]2-Microglobulin ([beta]2m) subunit with a human version. The nature of the [beta]2m subunit was demonstrated to profoundly affect the ability of MHC class I molecules to bind NK cell receptors. This effect Of [beta]2m may be indirect and occur through conformational changes in the MHC class I molecule. It may also be interpreted in favor of a direct interaction between Ly49 receptors and [beta]2m. Practically, as [beta]2m can be passively exchanged from serum in cellular in vitro culture systems, these data indicate that autologous serum should always be employed in functional assays. Finally, the mechanism of viral escape was dissected at a structural level, by solving the structures of two MHC class I alleles complexed with the same immunodominant peptide from lymphocytic choriomeningitis virus (LCMV), known to be selectively modified during the course of viral infection. The peptide bound the two MHC molecules in diametrically opposed conformations, where one side chain could serve as a downpointing anchor in one case and as a solvent exposed TCR residue in the other case. Through a single modification of an amino acid the virus is able to affect, in different but critical ways, the peptide binding or recognition of both MHC complexes which would otherwise be used to mount a protective cytolytic immune response. These data thus demonstrate that the functional consequences of subtle structural alterations may be enormous in a pathogen-host interplay, and that structural studies provide conclusive evidence to support other forms of investigative analysis.
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| 2. |
- Agback, Tatiana, et al.
(författare)
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Combined NMR and molecular dynamics conformational filter identifies unambiguously dynamic ensembles of Dengue protease NS2B/NS3pro
- 2023
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Ingår i: COMMUNICATIONS BIOLOGY. - 2399-3642. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- The dengue protease NS2B/NS3pro has been reported to adopt either an 'open' or a 'closed' conformation. We have developed a conformational filter that combines NMR with MD simulations to identify conformational ensembles that dominate in solution. Experimental values derived from relaxation parameters for the backbone and methyl side chains were compared with the corresponding back-calculated relaxation parameters of different conformational ensembles obtained from free MD simulations. Our results demonstrate a high prevalence for the 'closed' conformational ensemble while the 'open' conformation is absent, indicating that the latter conformation is most probably due to crystal contacts. Conversely, conformational ensembles in which the positioning of the co-factor NS2B results in a 'partially' open conformation, previously described in both MD simulations and X-ray studies, were identified by our conformational filter. Altogether, we believe that our approach allows for unambiguous identification of true conformational ensembles, an essential step for reliable drug discovery. A conformational filter that combines NMR with MD simulations to identify conformational ensembles that dominate in solution suggests dengue protease NS2B/NS3pro predominantly exists in a "closed" conformation.
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| 3. |
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| 4. |
- Anedda, Francesca, et al.
(författare)
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Multiple polymorphisms affect expression and function of the neuropeptide S receptor (NPSR1)
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:12, s. e29523-
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Tidskriftsartikel (refereegranskat)abstract
- Background: neuropeptide S (NPS) and its receptor NPSR1 act along the hypothalamic-pituitary-adrenal axis to modulate anxiety, fear responses, nociception and inflammation. The importance of the NPS-NPSR1 signaling pathway is highlighted by the observation that, in humans, NPSR1 polymorphism associates with asthma, inflammatory bowel disease, rheumatoid arthritis, panic disorders, and intermediate phenotypes of functional gastrointestinal disorders. Because of the genetic complexity at the NPSR1 locus, however, true causative variations remain to be identified, together with their specific effects on receptor expression or function. To gain insight into the mechanisms leading to NPSR1 disease-predisposing effects, we performed a thorough functional characterization of all NPSR1 promoter and coding SNPs commonly occurring in Caucasians (minor allele frequency >0.02). Principal Findings: we identified one promoter SNP (rs2530547 [-103]) that significantly affects luciferase expression in gene reporter assays and NPSR1 mRNA levels in human leukocytes. We also detected quantitative differences in NPS-induced genome-wide transcriptional profiles and CRE-dependent luciferase activities associated with three NPSR1 non-synonymous SNPs (rs324981 [Ile107Asn], rs34705969 [Cys197Phe], rs727162 [Arg241Ser]), with a coding variant exhibiting a loss-of-function phenotype (197Phe). Potential mechanistic explanations were sought with molecular modelling and bioinformatics, and a pilot study of 2230 IBD cases and controls provided initial support to the hypothesis that different cis-combinations of these functional SNPs variably affect disease risk. Significance: these findings represent a first step to decipher NPSR1 locus complexity and its impact on several human conditions NPS antagonists have been recently described, and our results are of potential pharmacogenetic relevance.
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| 5. |
- Borggren, Marie, et al.
(författare)
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Increased Sensitivity to Broadly Neutralizing Antibodies of End-Stage Disease R5 HIV-1 Correlates with Evolution in Env Glycosylation and Charge.
- 2011
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 6:6
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Tidskriftsartikel (refereegranskat)abstract
- Induction of broadly neutralizing antibodies, such as the monoclonal antibodies IgGb12, 2F5 and 2G12, is the objective of most antibody-based HIV-1 vaccine undertakings. However, despite the relative conserved nature of epitopes targeted by these antibodies, mechanisms underlying the sensitivity of circulating HIV-1 variants to broadly neutralizing antibodies are not fully understood. Here we have studied sensitivity to broadly neutralizing antibodies of HIV-1 variants that emerge during disease progression in relation to molecular alterations in the viral envelope glycoproteins (Env), using a panel of primary R5 HIV-1 isolates sequentially obtained before and after AIDS onset.
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| 6. |
- Brodin, Petter, et al.
(författare)
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Natural Killer Cell Tolerance Persists Despite Significant Reduction of Self MHC Class I on Normal Target Cells in Mice
- 2010
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 5:10, s. e13174-
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Tidskriftsartikel (refereegranskat)abstract
- Background: A major group of murine inhibitory receptors on Natural Killer (NK) cells belong to the Ly49 receptor family and recognize MHC class I molecules. Infected or transformed target cells frequently downmodulate MHC class I molecules and can thus avoid CD8(+) T cell attack, but may at the same time develop NK cell sensitivity, due to failure to express inhibitory ligands for Ly49 receptors. The extent of MHC class I downregulation needed on normal cells to trigger NK cell effector functions is not known. Methodology/Principal Findings: In this study, we show that cells expressing MHC class I to levels well below half of the host level are tolerated in an in vivo assay in mice. Hemizygous expression (expression from only one allele) of MHC class I was sufficient to induce Ly49 receptor downmodulation on NK cells to a similar degree as homozygous expression, despite a strongly reduced cell surface level of MHC class I. Co-expression of weaker MHC class I ligands in the host did not have any further effect on the degree of Ly49 downmodulation. Furthermore, a single MHC class I allele could downmodulate up to three Ly49 receptors on individual NK cells. Only when NK cells simultaneously expressed several Ly49 receptors and hemizygous MHC class I levels, a putative threshold for Ly49 downmodulation was reached. Conclusion: Collectively, our findings suggest that in interactions between NK cells and normal untransformed cells, MHC class I molecules are in most cases expressed in excess compared to what is functionally needed to ensure self tolerance and to induce maximal Ly49 downmodulation. We speculate that the reason for this is to maintain a safety margin for otherwise normal, autologous cells over a range of MHC class I expression levels, in order to ensure robustness in NK cell tolerance.
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| 7. |
- Burguillos Garcia, Miguel, et al.
(författare)
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Microglia-Secreted Galectin-3 Acts as a Toll-like Receptor 4 Ligand and Contributes to Microglial Activation.
- 2015
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Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 10:9, s. 1626-1638
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Tidskriftsartikel (refereegranskat)abstract
- Inflammatory response induced by microglia plays a critical role in the demise of neuronal populations in neuroinflammatory diseases. Although the role of toll-like receptor 4 (TLR4) in microglia's inflammatory response is fully acknowledged, little is known about endogenous ligands that trigger TLR4 activation. Here, we report that galectin-3 (Gal3) released by microglia acts as an endogenous paracrine TLR4 ligand. Gal3-TLR4 interaction was further confirmed in a murine neuroinflammatory model (intranigral lipopolysaccharide [LPS] injection) and in human stroke subjects. Depletion of Gal3 exerted neuroprotective and anti-inflammatory effects following global brain ischemia and in the neuroinflammatory LPS model. These results suggest that Gal3-dependent-TLR4 activation could contribute to sustained microglia activation, prolonging the inflammatory response in the brain.
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| 8. |
- Chao, Yashuan, et al.
(författare)
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The serine protease HtrA plays a key role in heat-induced dispersal of pneumococcal biofilms
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae (the pneumococcus) colonizes the human nasopharynx by forming multicellular biofilms. Due to the high level of asymptomatic carriage, transition to infections, such as otitis media, pneumonia, sepsis, and meningitis, occurs often enough that the pneumococcus remains a major cause of disease and death globally. Virus infection and virus-induced responses, such as increased temperature (fever), trigger release of virulent bacteria from colonizing biofilms. The exact mechanisms involved in pneumococcal egress during biofilm dispersal remain unknown, although we hypothesize that disruption of the biofilm matrix encasing the bacteria is necessary. Here, we utilized established in vitro biofilm dispersal models to investigate the involvement of proteases in bacterial egress from pneumococcal biofilms. We demonstrate the importance of protease activity, both through increased bacterial release following addition of proteases and reduced heat-induced biofilm dispersal in the presence of protease inhibitors. We identify a key role for the surface-exposed serine protease HtrA, but not PrtA, in heat-induced biofilm dispersal. Bacterial release from htrA-negative biofilms was significantly reduced compared to wild-type isogenic strains but was restored and increased above wild-type levels following addition of recombinant HtrA. Understanding the specific mechanisms involved in bacterial egress may provide novel targets for future strategies aimed to specifically interfere with disease progression without disturbing nasopharyngeal biofilm colonization.
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| 9. |
- Duru, Adil Doganay, et al.
(författare)
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Tuning antiviral CD8 T-cell response via proline-altered peptide ligand vaccination
- 2020
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Ingår i: PLoS Pathogens. - : PUBLIC LIBRARY SCIENCE. - 1553-7366 .- 1553-7374. ; 16:5
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Tidskriftsartikel (refereegranskat)abstract
- Viral escape from CD8(+) cytotoxic T lymphocyte responses correlates with disease progression and represents a significant challenge for vaccination. Here, we demonstrate that CD8(+) T cell recognition of the naturally occurring MHC-I-restricted LCMV-associated immune escape variant Y4F is restored following vaccination with a proline-altered peptide ligand (APL). The APL increases MHC/peptide (pMHC) complex stability, rigidifies the peptide and facilitates T cell receptor (TCR) recognition through reduced entropy costs. Structural analyses of pMHC complexes before and after TCR binding, combined with biophysical analyses, revealed that although the TCR binds similarly to all complexes, the p3P modification alters the conformations of a very limited amount of specific MHC and peptide residues, facilitating efficient TCR recognition. This approach can be easily introduced in peptides restricted to other MHC alleles, and can be combined with currently available and future vaccination protocols in order to prevent viral immune escape. Author summary Viral escape mutagenesis correlates often with disease progression and represents a major hurdle for vaccination-based therapies. Here, we have designed and developed a novel generation of altered epitopes that re-establish and enhance significantly CD8(+) T cell recognition of a naturally occurring viral immune escape variant. Biophysical and structural analyses provide a clear understanding of the molecular mechanisms underlying this reestablished recognition. We believe that this approach can be implemented to currently available or novel vaccination approaches to efficiently restore T cell recognition of virus escape variants to control disease progression.
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| 10. |
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