New insights into pb5, the receptor binding protein of bacteriophage T5, and its interaction with its Escherichia coli receptor FhuA

International audienceThe majority of bacterial viruses are bacteriophages bearing a tail that serves to recognise the bacterial surface and deliver the genome into the host cell. Infection is initiated by the irreversible interaction between the viral receptor binding protein (RBP) and a receptor at the surface of the bacterium. This interaction results ultimately in the phage DNA release in the host cytoplasm. Phage T5 infects Escher-ichia coli after binding of its RBP pb5 to the outer membrane ferrichrome transporter FhuA. Here, we have studied the complex formed by pb5 and FhuA by a variety of biophysical and biochemical techniques. We show that unlike RBPs of known structures, pb5 probably folds as a unique domain fulfilling both functions of binding to the host receptor and interaction with the rest of the phage. Pb5 likely binds to the domain occluding the b-barrel of FhuA as well as to external loops of the barrel. Furthermore, upon binding to FhuA, pb5 undergoes conformational changes, at the secondary and tertiary structure level that would be the key to the transmission of the signal through the tail to the capsid, triggering DNA release. This is the first structural information regarding the binding of a RBP to a proteic receptor. Ó 2012 Elsevier Masson SAS. All rights reserved

The use of Nile Red to monitor the aggregation behavior in ternary surfactant–water–organic solvent systems

Ternary systems of surfactants, water and organic solvents were studied by monitoring the steady-state fluorescence of the versatile solvatochromic probe Nile Red. We found not only that Nile Red can be used throughout the whole isotropic regions in the phase diagram, but also that subtle changes in the aggregation state of the surfactant can be monitored. The formation of inverted micelles in n-hexane could be followed upon the addition of small amounts of water, in addition to the formation of normal micelles in water and water–organic solvent mixtures. In aqueous C12EO4 solutions the temperature-dependent micelle-to-vesicle-to-inverted micelle transition was visualized by Nile Red fluorescence. Finally, the incorporation of solvent into the micellar interior could also be monitored using Nile Red as the probe.

Directing peptide crystallization through curvature control of nanotubes ‡

International audienceIn the absence of efficient crystallization methods, the molecular structures of fibrous assemblies have so far remained rather elusive. In this paper, we present a rational method to crystallize the lanreotide octapeptide by modification of a residue involved in a close contact. Indeed, we show that it is possible to modify the curvature of the lanreotide nanotubes and hence their diameter. This fine tuning leads to crystallization because the radius of curvature of the initially bidimensional peptide wall can be increased up to a point where the wall is essentially flat and a crystal is allowed to grow along a third dimension. By comparing X-ray diffraction data and Fourier transform Raman spectra, we show that the nanotubes and the crystals share similar cell parameters and molecular conformations, proving that there is indeed a structural continuum between these two morphologies. These results illustrate a novel approach to crystallization and represent the first step towards the acquisition of an Å-resolution structure of the lanreotide nanotubes β-sheet assembly

Proton Motive Force-Dependent Hoechst 33342 Transport by the ABC Transporter LmrA of Lactococcus lactis

The fluorescent compound Hoechst 33342 is a substrate for many multidrug resistance (MDR) transporters and is widely used to characterize their transport activity. We have constructed mutants of the adenosine triphosphate (ATP) binding cassette (ABC)-type MDR transporter LmrA of Lactococcus lactis that are defective in ATP hydrolysis. These mutants and wild-type LmrA exhibited an atypical behavior in the Hoechst 33342 transport assay. In membrane vesicles, Hoechst 33342 transport was shown to be independent of the ATPase activity of LmrA, and it was not inhibited by orthovanadate but sensitive to uncouplers that collapse the proton gradient and to N,N'-dicyclohexylcarbodiimide, an inhibitor of the F0F1-ATPase. In contrast, transport of Hoechst 33342 by the homologous, heterodimeric MDR transporter LmrCD showed a normal ATP dependence and was insensitive to uncouplers of the proton gradient. With intact cells, expression of LmrA resulted in an increased rate of Hoechst 33342 influx while LmrCD caused a decrease in the rate of Hoechst 33342 influx. Cellular toxicity assays using a triple knockout strain, i.e., L. lactis ΔlmrA ΔlmrCD, demonstrate that expression of LmrCD protects cells against the growth inhibitory effects of Hoechst 33342, while in the presence of LmrA, cells are more susceptible to Hoechst 33342. Our data demonstrate that the LmrA-mediated Hoechst 33342 transport in membrane vesicles is influenced by the transmembrane pH gradient due to a pH-dependent partitioning of Hoechst 33342 into the membrane.

Écritures de la mémoire / Mémoires de l’écriture: JEHANNE PATERNOSTRE

Pg. 19 à 2

La géologie souterraine de la Grotte de Han (Rochefort, Belgique)

editorial reviewed4. Quality education6. Clean water and sanitation13. Climate actio

Correlation between lithostratigraphy and karstic speleothems at the cave of Han-sur-Lesse (Rochefort, Belgium)

editorial reviewedThe objective of this study is to investigate the correlation between speleothems (secondary carbonate deposits in caves) and rocks in which they were formed in the cave of Han-sur-Lesse in Belgium. To answer this problematic, a lithostratigraphic study of the Givetian host rock in which the speleothems were set up was based mainly on the studies of (Bultynck et al, 1991 and Coen & Coen Aubert, 1971). The study showed that the geological Formations present in the cave (Touristic network and “Réseau Sud”) are essentially those of Mont d’Haurs and Fromelennes (composed by Moulin Boreux and Flohimont Members in this cave). This study precisely locate the limits of Flohimont Member in the Artificial tunnel (Touristic network) and locate it entirely in the “Salle de la Pentecôte” (“Réseau Sud”).4. Quality education11. Sustainable cities and communities6. Clean water and sanitatio

Correlation test between lithostratigraphy and karstic speleothems at the caves of Han-sur-Lesse (Rochefort, Belgium)

editorial reviewed13. Climate actio