13 research outputs found
Novel STAT1 Alleles in Otherwise Healthy Patients with Mycobacterial Disease
The transcription factor signal transducer and activator of transcription-1 (STAT1) plays a key role in immunity against mycobacterial and viral infections. Here, we characterize three human STAT1 germline alleles from otherwise healthy patients with mycobacterial disease. The previously reported L706S, like the novel Q463H and E320Q alleles, are intrinsically deleterious for both interferon gamma (IFNG)–induced gamma-activating factor–mediated immunity and interferon alpha (IFNA)–induced interferon-stimulated genes factor 3–mediated immunity, as shown in STAT1-deficient cells transfected with the corresponding alleles. Their phenotypic effects are however mediated by different molecular mechanisms, L706S affecting STAT1 phosphorylation and Q463H and E320Q affecting STAT1 DNA-binding activity. Heterozygous patients display specifically impaired IFNG-induced gamma-activating factor–mediated immunity, resulting in susceptibility to mycobacteria. Indeed, IFNA-induced interferon-stimulated genes factor 3–mediated immunity is not affected, and these patients are not particularly susceptible to viral disease, unlike patients homozygous for other, equally deleterious STAT1 mutations recessive for both phenotypes. The three STAT1 alleles are therefore dominant for IFNG-mediated antimycobacterial immunity but recessive for IFNA-mediated antiviral immunity at the cellular and clinical levels. These STAT1 alleles define two forms of dominant STAT1 deficiency, depending on whether the mutations impair STAT1 phosphorylation or DNA binding
Most residues on the floor of the antigen binding site of the class I MHC molecule H-2Kd influence peptide presentation.
A panel of 15 single alanine substitutions on the floor of the peptide binding groove of the murine class I histocompatibility molecule H-2Kd has been analyzed. All but two mutant molecules were expressed on the cell surface, and were tested for peptide binding and presentation to specific cytotoxic T lymphocytes. Eleven out of 13 mutant molecules appeared to be functionally altered. Five of the substituted residues were involved in the presentation of all peptides tested. Three participated in the presentation of certain peptides but not others. Three other residues participated in epitope formation through indirect interactions. Only two mutations had no detectable effect
Structural information on a cecropin-like synthetic peptide, Shiva-3 toxic to the sporogonic development of Plasmodium berghei.
International audienceThis study is a contribution towards the understanding of the mode of action of Shiva-3 and more generally that of cecropin-like peptides. Structural information on Shiva-3 (a cecropin-like synthetic peptide) in water and in a membrane-mimicking environment (trifluoroethanol alcohol, SDS) were obtained using analytical centrifugation, CD and NMR spectroscopies. A total of 20 converged structures were retained on the basis of 197 non-redundant experimental constraints, including 166 distance constraints from the nuclear Overhauser effect measurements and 31 dihedral angle restraints derived from the purged COSY experiments. Some results obtained in presence of SDS are also presented. The toxic effects of the peptides obtained by cleavage (trypsin and lysine-C hydrolysis) of Shiva-3 on Escherichia coli and on Plasmodium berghei sporogonic stages are reported. Biological effects are discussed in relation to the calculated structure. The antiparasite activity and the low mosquito toxicity of Shiva-3 make this peptide a good candidate for genetic transformation of mosquito vectors which warrants further studies aimed at the improvement of the molecule
Optimization of virulence functions through glucosylation of Shigella LPS
Shigella, the leading cause of bacillary dysentery, uses a type III secretion system (TTSS) to inject proteins into human cells, leading to bacterial invasion and a vigorous inflammatory response. The bacterium is protected against the response by the O antigen of lipopolysaccharide (LPS) on its surface. We show that bacteriophage-encoded glucosylation of Shigella O antigen, the basis of different serotypes, shortens the LPS molecule by around half. This enhances TTSS function without compromising the protective properties of the LPS. Thus, LPS glucosylation promotes bacterial invasion and evasion of innate immunity, which may have contributed to the emergence of serotype diversity in Shigella
Structural basis of the signalling through a bacterial membrane receptor HasR deciphered by an integrative approach
Bacteria use diverse signalling pathways to adapt gene expression to external stimuli. In Gram-negative bacteria, the binding of scarce nutrients to membrane transporters triggers a signalling process that up-regulates the expression of genes of various functions, from uptake of nutrient to production of virulence factors. Although proteins involved in this process have been identified, signal transduction through this family of transporters is not well understood. In the present study, using an integrative approach (EM, SAXS, X-ray crystallography and NMR), we have studied the structure of the haem transporter HasR captured in two stages of the signalling process, i.e. before and after the arrival of signalling activators (haem and its carrier protein). We show for the first time that the HasR domain responsible for signal transfer: (i) is highly flexible in two stages of signalling; (ii) extends into the periplasm at approximately 70–90 Å (1 Å=0.1 nm) from the HasR β-barrel; and (iii) exhibits local conformational changes in response to the arrival of signalling activators. These features would favour the signal transfer from HasR to its cytoplasmic membrane partners