Conformational and thermodynamic changes of the repressor/DNA operator complex upon monomerization shed new light on regulation mechanisms of bacterial resistance against β-lactam antibiotics

In absence of β-lactam antibiotics, BlaI and MecI homodimeric repressors negatively control the expression of genes involved in β-lactam resistance in Bacillus licheniformis and in Staphylococcus aureus. Subsequently to β-lactam presence, BlaI/MecI is inactivated by a single-point proteolysis that separates its N-terminal DNA-binding domain to its C-terminal domain responsible for its dimerization. Concomitantly to this proteolysis, the truncated repressor acquires a low affinity for its DNA target that explains the expression of the structural gene for resistance. To understand the loss of the high DNA affinity of the truncated repressor, we have determined the different dissociation constants of the system and solved the solution structure of the B. licheniformis monomeric repressor complexed to the semi-operating sequence OP1 of blaP (1/2OP1blaP) by using a de novo docking approach based on inter-molecular nuclear Overhauser effects and chemical-shift differences measured on each macromolecular partner. Although the N-terminal domain of the repressor is not subject to internal structural rearrangements upon DNA binding, the molecules adopt a tertiary conformation different from the crystallographic operator–repressor dimer complex, leading to a 30° rotation of the monomer with respect to a central axis extended across the DNA

A Peptidoglycan Fragment Triggers β-lactam Resistance in Bacillus licheniformis

To resist to β-lactam antibiotics Eubacteria either constitutively synthesize a β-lactamase or a low affinity penicillin-binding protein target, or induce its synthesis in response to the presence of antibiotic outside the cell. In Bacillus licheniformis and Staphylococcus aureus, a membrane-bound penicillin receptor (BlaR/MecR) detects the presence of β-lactam and launches a cytoplasmic signal leading to the inactivation of BlaI/MecI repressor, and the synthesis of a β-lactamase or a low affinity target. We identified a dipeptide, resulting from the peptidoglycan turnover and present in bacterial cytoplasm, which is able to directly bind to the BlaI/MecI repressor and to destabilize the BlaI/MecI-DNA complex. We propose a general model, in which the acylation of BlaR/MecR receptor and the cellular stress induced by the antibiotic, are both necessary to generate a cell wall-derived coactivator responsible for the expression of an inducible β-lactam-resistance factor. The new model proposed confirms and emphasizes the role of peptidoglycan degradation fragments in bacterial cell regulation

Simple scoring system to predict in-hospital mortality after surgery for infective endocarditis

BACKGROUND: Aspecific scoring systems are used to predict the risk of death postsurgery in patients with infective endocarditis (IE). The purpose of the present study was both to analyze the risk factors for in-hospital death, which complicates surgery for IE, and to create a mortality risk score based on the results of this analysis. METHODS AND RESULTS: Outcomes of 361 consecutive patients (mean age, 59.1\ub115.4 years) who had undergone surgery for IE in 8 European centers of cardiac surgery were recorded prospectively, and a risk factor analysis (multivariable logistic regression) for in-hospital death was performed. The discriminatory power of a new predictive scoring system was assessed with the receiver operating characteristic curve analysis. Score validation procedures were carried out. Fifty-six (15.5%) patients died postsurgery. BMI >27 kg/m2 (odds ratio [OR], 1.79; P=0.049), estimated glomerular filtration rate 55 mm Hg (OR, 1.78; P=0.032), and critical state (OR, 2.37; P=0.017) were independent predictors of in-hospital death. A scoring system was devised to predict in-hospital death postsurgery for IE (area under the receiver operating characteristic curve, 0.780; 95% CI, 0.734-0.822). The score performed better than 5 of 6 scoring systems for in-hospital death after cardiac surgery that were considered. CONCLUSIONS: A simple scoring system based on risk factors for in-hospital death was specifically created to predict mortality risk postsurgery in patients with IE

Le diagnostic d'homocystinurie à l'âge adulte (à propos de six cas extraits d'une étude de l'homocystinurie dans la population française)

MONTPELLIER-BU Médecine UPM (341722108) / SudocPARIS-BIUM (751062103) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Thromboses veineuses profondes du membre supérieur

MONTPELLIER-BU Médecine UPM (341722108) / SudocPARIS-BIUM (751062103) / SudocMONTPELLIER-BU Médecine (341722104) / SudocSudocFranceF

Prise en charge des patients hypercholestérolémiques en Médecine Génerale (enquête en Aquitaine)

BORDEAUX2-BU Santé (330632101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Solution structural study of BlaI: implications for the repression of genes involved in beta-lactam antibiotic resistance.

beta-Lactamase and penicillin-binding protein PBP2' mediate staphylococcal resistance to beta-lactam antibiotics, which are otherwise highly clinically effective. Two repressors (BlaI and MecI) regulate expression of these inducible proteins. Here, we present the first solution structure of the 82 amino acid residue DNA-binding domain of Bacillus licheniformis BlaI which is very similar in primary sequence to the medically significant Staphyloccocal BlaI and MecI proteins. This structure is composed of a compact core of three alpha-helices and a three-stranded beta-sheet typical of the winged helix protein (WHP) family. The protein/DNA complex was studied by NMR chemical shift comparison between the free and complexed forms of BlaI. Residues involved in DNA interaction were identified and a WHP canonical model of interaction with the operators is proposed. In this model, specific contacts occur between the base-pairs of the TACA motif and conserved amino acid residues of the repressor helix H3. These results help toward understanding the repression and induction mechanism of the genes coding for beta-lactamase and PBP2'

Toward the characterization of peptidoglycan structure and protein-peptidoglycan interactions by solid-state NMR spectroscopy.

Solid-state NMR spectroscopy is applied to intact peptidoglycan sacculi of the Gram-negative bacterium Escherichia coli. High-quality solid-state NMR spectra allow atom-resolved investigation of the peptidoglycan structure and dynamics as well as the study of protein-peptidoglycan interactions

1H, 13C and 15N resonance assignments of YajG, an Escherichia coli protein of unknown structure and function.

The ampG gene codes for a permease required to uptake anhydro-muropeptides into bacterial cytoplasm. Located upstream in the same operon, is another 579-base-pair-long open reading frame encoding a putative lipoprotein YajG, whose nearly complete 1H,13C,15N assignments are reported here