Interplays between copper and Mycobacterium tuberculosis GroEL1

The recalcitrance of pathogenic Mycobacterium tuberculosis, the agent of tuberculosis, to eradication is due to various factors allowing bacteria to escape from stress situations. The mycobacterial chaperone GroEL1, overproduced after macrophage entry and under oxidative stress, could be one of these key players. We previously reported that GroEL1 is necessary for the biosynthesis of phthiocerol dimycocerosate, a virulence-associated lipid and for reducing antibiotic susceptibility. In the present study, we showed that GroEL1, bearing a unique C-terminal histidine-rich region, is required for copper tolerance during Mycobacterium bovis BCG biofilm growth. Mass spectrometry analysis demonstrated that GroEL1 displays high affinity for copper ions, especially at its C-terminal histidine-rich region. Furthermore, the binding of copper protects GroEL1 from destabilization and increases GroEL1 ATPase activity. Altogether, these findings suggest that GroEL1 could counteract copper toxicity, notably in the macrophage phagosome, and further emphasizes that M. tuberculosis GroEL1 could be an interesting antitubercular target

A large decrease in heat-shock-induced proteolysis after tryptophan starvation leads to increased expression of phage lambda lysozyme cloned in Escherichia coli.

The R gene coding for phage lambda lysozyme (lambda L), cloned under the control of the PL promoter on a multicopy vector, is expressed in an Escherichia coli strain auxotrophic for tryptophan. Induction by a thermal shift after tryptophan supplementation in a culture initially brought into stationary phase by tryptophan starvation leads to highly increased expression. A thermally unstable mutant protein, difficult to obtain under standard conditions, can be easily produced by post-stationary-phase expression. It is shown that this is due to a drastic decrease in the heat-shock-induced proteolysis normally observed on thermal induction. These data are discussed in relation to our present knowledge of stringent and heat-shock responses

Electron-transfer Photoinduced From Naphtholate Anions - Anion Oxidation Potentials and Use of Marcus Free-energy Relationships

The fluorescing excited states of four naphtholate type anions are quenched by various acceptors according to an electron-transfer mechanism. By use of the Marcus free energy relationship, the electron-transfer rate constants were correlated with the reduction potentials of the acceptors and a first set of oxidation potentials (around 0.5 V) was estimated for the anions. The fluorescence of perylene was quenched by the naphtholate anions but a second set of oxidation potentials, different from the preceeding one was obtained for the anions (around 1 V). The difference was rationalized by considering that a hydrogen bond between the anion and the solvent is broken during the excitation when the anions are in their excited states. The hydrogen bond is broken during the electron-transfer quenching when the naphtholate anions are in their ground states. This implies, in the first case, an intrinsic activation barrier, taking the H bond rupture into account. In the second case, the fraction of the excitation energy available for electron transfer must be evaluated. The oxidation potentials after correction were finally estimated around 0.8 V. In DMF, the oxidation potential of the 2-naphtholate anion is found to be decreased (around 0.1 V) and this is probably related to the lack of any hydrogen bonding in this solvent. The use of the Marcus model and the possibility of measuring in the inverted Marcus region are discussed