Structural and Genetic Analyses Reveal a Key Role in Prophage Excision for the TorI Response Regulator Inhibitor

International audienceTorI (Tor inhibition protein) has been identified in Escherichia coli as a protein inhibitor acting through protein-protein interaction with the TorR response regulator. This interaction, which does not interfere with TorR DNA binding activity, probably prevents the recruitment of RNA polymerase to the torC promoter. In this study we have solved the solution structure of TorI, which adopts a prokaryotic winged-helix arrangement. Despite no primary sequence similarity, the three-dimensional structure of TorI is highly homologous to the Xis, Mu bacteriophage repressor (MuR-DBD), and transposase (MuA-DBD) structures. We propose that the TorI protein is the structural missing link between the Xis and MuR proteins. Moreover, in vivo assays demonstrated that TorI plays an essential role in prophage excision. Heteronuclear NMR experiments and site-directed mutagenesis studies have pinpointed out key residues involved in the DNA binding activity of TorI. Our findings suggest that TorI-related proteins identified in various pathogenic bacterial genomes define a new family of atypical excisionases

Electrostatic interactions between the CTX phage minor coat protein and the bacterial host receptor TolA drive the pathogenic conversion of Vibrio cholerae

International audienceVibrio cholerae is a natural inhabitant of aquatic environments and converts to a pathogen upon infection by a filamentous phage, CTXΦ, that transmits the cholera toxin encoding genes. This toxigenic conversion of V. cholerae has evident implication in both genome plasticity and epidemic risk, but the early stages of the infection have not been thoroughly studied. CTXΦ transit across the bacterial periplasm requires binding between the minor coat protein named pIII and a bacterial inner-membrane receptor, TolA, which is part of the conserved Tol-Pal molecular motor. To gain insight into the TolA-pIII complex, we developed a bacterial two-hybrid approach, named Oxi-BTH, suited for studying the interactions between disulfide bond-folded proteins in the bacterial cytoplasm of an E. coli reporter strain. We found that two of the four disulfide bonds of pIII are required for its interaction with TolA. By combining Oxi-BTH assays, NMR, and genetic studies, we also demonstrate that two intermolecular salt bridges between TolA and pIII provide the driving forces of the complex interaction. Moreover, we show that TolA residue R325 involved in one of the two salt bridges is critical for proper functioning of the Tol-Pal system. Our results imply that to prevent host evasion, CTXΦ uses an infection strategy that targets a highly conserved protein of Gram-negative bacteria essential for the fitness of V. cholerae in its natural environment

(1)H, (15)N and (13)C resonance assignments of the C-terminal domain of Vibrio cholerae TolA protein.

International audienceVibrio cholerae is the bacterial causative agent of the human disease cholera. Non-pathogenic bacterium can be converted to pathogenic following infection by a filamentous phage, CTX?, that carries the cholera toxin encoding genes. A crucial step during phage infection requires a direct interaction between the CTX? minor coat protein (pIII(CTX)) and the C-terminal domain of V. cholerae TolA protein (TolAIIIvc). In order to get a better understanding of TolA function during the infection process, we have initiated a study of the V. cholerae TolAIII domain by 2D and 3D heteronuclear NMR. With the exception of the His-tag (H123-H128), 97 % of backbone (1)H, (15)N and (13)C resonances were assigned and the side chain assignments for 92 % of the protein were obtained (BMRB deposit with accession number 25689)

Effects of the Tyr64 Substitution on the Stability of Cytochrome c553, a low Oxidoreduction-Potential Cytochrome from Desulfovibrio vulgaris Hildenborough

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Structural and functional characterization of the Clostridium perfringens N-acetylmannosamine-6-phosphate 2-epimerase essential for the sialic acid salvage pathway.

International audiencePathogenic bacteria are endowed with an arsenal of specialized enzymes to convert nutrient compounds from their cell hosts. The essential N-acetylmannosamine-6-phosphate 2-epimerase (NanE) belongs to a convergent glycolytic pathway for utilization of the three amino sugars, GlcNAc, ManNAc, and sialic acid. The crystal structure of ligand-free NanE from Clostridium perfringens reveals a modified triose-phosphate isomerase (?/?)8 barrel in which a stable dimer is formed by exchanging the C-terminal helix. By retaining catalytic activity in the crystalline state, the structure of the enzyme bound to the GlcNAc-6P product identifies the topology of the active site pocket and points to invariant residues Lys(66) as a putative single catalyst, supported by the structure of the catalytically inactive K66A mutant in complex with substrate ManNAc-6P. (1)H NMR-based time course assays of native NanE and mutated variants demonstrate the essential role of Lys(66) for the epimerization reaction with participation of neighboring Arg(43), Asp(126), and Glu(180) residues. These findings unveil a one-base catalytic mechanism of C2 deprotonation/reprotonation via an enolate intermediate and provide the structural basis for the development of new antimicrobial agents against this family of bacterial 2-epimerases

Glycan dependence of Galectin-3 self-association properties.

Human Galectin-3 is found in the nucleus, the cytoplasm and at the cell surface. This lectin is constituted of two domains: an unfolded N-terminal domain and a C-terminal Carbohydrate Recognition Domain (CRD). There are still uncertainties about the relationship between the quaternary structure of Galectin-3 and its carbohydrate binding properties. Two types of self-association have been described for this lectin: a C-type self-association and a N-type self-association. Herein, we have analyzed Galectin-3 oligomerization by Dynamic Light Scattering using both the recombinant CRD and the full length lectin. Our results proved that LNnT induces N-type self-association of full length Galectin-3. Moreover, from Nuclear Magnetic Resonance (NMR) and Surface Plasmon Resonance experiments, we observed no significant specificity or affinity variations for carbohydrates related to the presence of the N-terminal domain of Galectin-3. NMR mapping clearly established that the N-terminal domain interacts with the CRD. We propose that LNnT induces a release of the N-terminal domain resulting in the glycan-dependent self-association of Galectin-3 through N-terminal domain interactions

1H, 13C and 15N backbone and side-chain chemical shift assignments for reduced unusual thioredoxin Patrx2 of Pseudomonas aeruginosa.

International audienceThe gram-negative organism Pseudomonas aeruginosa is an opportunistic human pathogen and a leading cause of hospital-acquired infections. In P. aeruginosa PAO1, three cytoplasmic thioredoxins have been identified. An unusual thioredoxin (Patrx2) (108 amino acids) encoded by the PA2694 gene, is identified as a new thioredoxin-like protein based on sequence homology. Thioredoxin is a ubiquitous protein, which serves as a general protein disulfide oxidoreductase. Patrx2 present an atypical active site CGHC. We report the nearly complete (1)H, (13)C and (15)N resonance assignments of reduced Patrx2. 2D and 3D heteronuclear NMR experiments were performed with uniformly (15)N-, (13)C-labelled Patrx2, resulting in 97.2% backbone and 92.5% side-chain (1)H, (13)C and (15)N resonance assignments for the reduced form. (BMRB deposits with accession number 18130)

1H, 13C and 15N assignments of the C-terminal intrinsically disordered cytosolic fragment of the receptor tyrosine kinase ErbB2

International audienceErbB2 (or HER2) is a receptor tyrosine kinase that is involved in signaling pathways controlling cell division, motility and apoptosis. Though important in development and cell growth homeostasis, this protein, when overexpressed, participates in triggering aggressive HER2+ breast cancers. It is composed of an extracellular part and a transmembrane domain, both important for activation by dimerization, and a cytosolic tyrosine kinase, which activates its intrinsically disordered C-terminal end (CtErbB2). Little is known about this C-terminal part of 268 residues, despite its crucial role in interacting with adaptor proteins involved in signaling. Understanding its structural and dynamic characteristics could eventually lead to the design of new interaction inhibitors, and treatments complementary to those already targeting other parts of ErbB2. Here we report backbone and side-chain assignment of CtErbB2, which, together with structural predictions, confirms its intrinsically disordered nature

Zinc Binds to RRM2 Peptide of TDP-43

International audienceTransactive response DNA and RNA binding protein 43 kDa (TDP-43) is a highly conserved heterogeneous nuclear ribonucleoprotein (hnRNP), which is involved in several steps of protein production including transcription and splicing. Its aggregates are frequently observed in motor neurons from amyotrophic lateral sclerosis patients and in the most common variant of frontotemporal lobar degeneration. Recently it was shown that TDP-43 is able to bind Zn 2+ by its RRM domain. In this work, we have investigated Zn 2+ binding to a short peptide 256-264 from C-terminus of RRM2 domain using isothermal titration calorimetry, electrospray ionization mass spectrometry, QM/MM simulations, and NMR spectroscopy. We have found that this peptide is able to bind zinc ions with a K a equal to 1.6 × 10 5 M −1. Our findings suggest the existence of a zinc binding site in the C-terminal region of RRM2 domain. Together with the existing structure of the RRM2 domain of TDP-43 we propose a model of its complex with Zn 2+ which illustrates how zinc might regulate DNA/RNA binding

Chemical shift mapping representation on Galectin-3 CRD structure.

<p>A] Effects of the N-terminal domain on the NH groups of amino acids of the CRD. The structure of CRD in the presence of LNnT (PDB 4LBN) is shown. In yellow is Trp181, in red is LNnT and in blue are the amino acids of the CRD with chemical shift variations in the presence of the N-terminal domain within the full length Galectin-3. B] Effects of lactose on the NH groups of amino acids of the CRD. The structure of CRD in the presence of lactose (PDB 3ZSJ) is shown. In yellow is Trp181, in red is the lactose and in green are amino acids of CRD with chemical shift variations induced by the presence of lactose. C] Effects of LNnT on the NH groups of amino acids of the CRD. The structure of CRD in the presence of LNnT (PDB 4LBN) is shown. In yellow is Trp181, in red is LNnT and in green are amino acids of the CRD with chemical shift variations induced by the presence of LNnT.</p