The Colloidal State of Tannins Impacts the Nature of Their Interaction with Proteins: The Case of Salivary Proline-Rich Protein/Procyanidins Binding

While the definition of tannins has been historically associated with its propensity to bind proteins in a nonspecific way, it is now admitted that specific interaction also occurs. The case of the astringency perception is a good example to illustrate this phenomenon: astringency is commonly described as a tactile sensation induced by the precipitation of a complex composed of proline-rich proteins present in the human saliva and tannins present in beverages such as tea or red wines. In the present work, the interactions between a human saliva protein segment and three different procyanidins (B1, B3, and C2) were investigated at the atomic level by NMR and molecular dynamics. The data provided evidence for (i) an increase in affinity compared to shortest human saliva peptides, which is accounted for by protein “wraping around” the tannin, (ii) a specificity in the interaction below tannin critical micelle concentration (CMC) of ca. 10 mM, with an affinity scale such that C2 > B1 > B3, and (iii) a nonspecific binding above tannin CMC that conducts irremediably to the precipitation of the tannins/protein complex. Such physicochemical findings describe in accurate terms saliva protein–tannin interactions and provide support for a more subtle description by oenologists of wine astringency perception in the mouth

Biochimica et biophysica acta

Cell-penetrating peptides (CPP) are able to efficiently transport cargos across cell membranes without being cytotoxic to cells, thus present a great potential in drug delivery and diagnosis. While the role of cationic residues in CPPs has been well studied, that of Trp is still not clear. Herein 7 peptide analogs of RW9 (RRWWRRWRR, an efficient CPP) were synthesized in which Trp were systematically replaced by Phe residues. Quantification of cellular uptake reveals that substitution of Trp by Phe strongly reduces the internalization of all peptides despite the fact that they strongly accumulate in the cell membrane. Cellular internalization and biophysical studies show that not only the number of Trp residues but also their positioning in the helix and the size of the hydrophobic face they form are important for their internalization efficacy, the highest uptake occurring for the analog with 3 Trp residues. Using CD and ATR-FTIR spectroscopy we observe that all peptides became structured in contact with lipids, mainly in alpha-helix. Intrinsic tryptophan fluorescence studies indicate that all peptides partition in the membrane in about the same manner (Kp~10(5)) and that they are located just below the lipid headgroups (~10A) with slightly different insertion depths for the different analogs. Plasmon Waveguide Resonance studies reveal a direct correlation between the number of Trp residues and the reversibility of the interaction following membrane washing. Thus a more interfacial location of the CPP renders the interaction with the membrane more adjustable and transitory enhancing its internalization ability

Variability in secondary structure of the antimicrobial peptide Cateslytin in powder, solution, DPC micelles and at the air-water interface.

International audienceCateslytin (bCGA (344)RSMRLSFRARGYGFR(358)), a five positively charged 15 amino-acid residues arginine-rich antimicrobial peptide, was synthesized using a very efficient procedure leading to high yields and to a 99% purity as determined by HPLC and mass spectrometry. Circular dichroism, polarized attenuated total reflectance fourier transformed infrared, polarization modulation infrared reflection Absorption spectroscopies and proton two-dimensional NMR revealed the flexibility of such a peptide. Whereas being mostly disordered as a dry powder or in water solution, the peptide acquires a alpha-helical character in the "membrane mimicking" solvent trifuoroethanol. In zwitterionic micelles of dodecylphophatidylcholine the helical character is retained but to a lesser extent, the peptide returning mainly to its disordered state. A beta-sheet contribution of almost 100% is detected at the air-water interface. Such conformational plasticity is discussed regarding the antimicrobial action of Cateslytin

Dynamiques européennes. Nouvel espace, nouveaux acteurs

Les échecs de la construction européenne font plus de bruit que ses succès. Les blocages de l’Europe sont patents et, pourtant, l’Europe avance encore, car elle s’appuie depuis le milieu du XXe siècle sur une « dynamique » ou un ensemble de « dynamiques » intéressantes à analyser dans leur complexité. Les chercheurs qui ont contribué au présent ouvrage ont concentré leur réflexion sur cette notion de « dynamique européenne » en scrutant une période décisive, celle des années soixante-dix et du début des années quatre-vingt. Avec l’élargissement de la Communauté européenne, de nouveaux acteurs entrent en scène, un nouvel espace se dessine, de nouveaux enjeux s’imposent. Une identité nouvelle est même affirmée à la conférence de Copenhague en 1973, une identité politique communautaire, différente de la vieille et classique identité culturelle européenne. En outre, avec la « détente » entre l’Est et l’Ouest et le processus d’Helsinki, l’Autre Europe, celle de l’autre côté du rideau de fer, est dès cette époque concernée par la dynamique d’échanges intra-européens. L’étude de ces changements déterminants, qui ont contribué à modeler l’Europe d’aujourd’hui, a été développée lors d’un colloque organisé à Oxford, sous la direction d’Élisabeth du Réau (École doctorale « Espace européen contemporain », Paris III), d’Anne Deighton (St Anthony College, Oxford) et de Robert Frank (Institut Pierre Renouvin, Paris I), dans le cadre du vaste réseau international d’historiens travaillant sur « Les identités européennes au XXe siècle »