Bernard Michels

Evidence of micelle growth in aqueous solutions of the amphiphilic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers from differential scanning microcalorimetry

Abstract The aqueous solutions of two poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers, the Pluronic P84 (E 19 P 43 E 19 ) and P85 (E 26 P 40 E 26 ) where E=ethylene oxide and P=propylene oxide, have been investigated by DSC (differential scanning microcalorimetry). The DSC scans of aqueous solutions of both copolymers show three endothermal peaks, a large one at low temperature and two others of smaller amplitude at higher temperature. As in previous studies the first and third peaks have been unambiguously attributed to micelle formation and to clouding (phase separation), respectively. Reported studies of P85 permitted us to assign the second DSC peak to micelle growth , and not to the sol–gel transition which occurs at a slightly higher temperature. For P84, complementary investigations by means of turbidimetry, light scattering, and rheological methods permitted us to show that the middle DSC peak is also due to micelle growth. The middle peak had not been observed in previous DSC studies of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymers.

Heat-induced Conversion of Ovalbumin into a Proteinase Inhibitor

Ovalbumin is a member of the serine proteinase inhibitor (serpin) family but is unable to inhibit proteinases. Here we show that heating transforms it into inhibitory ovalbumin (I-ovalbumin), a potent reversible competitive inhibitor of human neutrophil elastase (Ki = 5 nM) and cathepsin G (Ki = 60 nM) and bovine chymotrypsin (Ki = 30 nM). I-ovalbumin also inhibits bovine trypsin, porcine elastase and α-lytic proteinase with Ki values in the micromolar range. Thus, I-ovalbumin differs from active serpins by its inability to form irreversible complexes with proteinases. I-ovalbumin is unusually thermostable: it does not undergo any structural transition between 45°C and 120°C as tested by differential scanning calorimetry, and it retains full inhibitory capacity after heating at 120°C. It has 8% less α-helices and 9% more β-sheet structures than native ovalbumin, as shown by circular dichroism. Our results show that the primary sequence of ovalbumin contains the information required for enabling the first step of the serpin-proteinase interaction to occur, i.e. the formation of the Michaelis-like reversible complex, but does not contain the information needed for stabilizing this initial complex.

Binding of nystatin and amphotericin B with sterol-free l-dilauroylphosphatidylcholine bilayers resulting in the formation of dichroic lipid superstructures

Interactions of multilamellar vesicles (MLV) of dilauroylphosphatidylcholine (DLPC) with the polyene antibiotics, amphotericin B (AmB) and nystatin (Ny), were followed by circular dichroism (CD). These interactions proceed with both antibiotics through a slow association with high [DLPC]/[antibiotic] stoichiometric molar ratios (> or = 130), at room temperature for which DLPC membranes are in a fluid state. Microscopic investigations of the spatial distributions of the antibiotic and the MLV in the mixtures revealed that MLV form clusters inside which the antibiotic is strongly concentrated and lipid superstructures appear. Concomitantly with the appearance of these superstructures a DLPC dichroic signal emerges. This observation indicates that the chiral properties of antibiotic oligomers can induce a chirality of the DLPC molecules which are bound to them. These results support the hypothesis of a recent molecular modeling of AmB oligomers which postulates that their chiral properties result from a chiral assemblage of antibiotic molecules (Millié et al., J. Phys. Chem. B, in press).

The formation of empty shells upon pressure induced decapsidation of turnip yellow mosaic virus

Summary. The stability of turnip yellow mosaic virus (TYMV) was investigated under pressure, using solution neutron small angle scattering. Dissociation products were characterized by analytical ultracentrifugation and electron microscopy. At pH 6.0, TYMV remained unaffected by pressure, up to 260 Megapascals (MPa), the highest pressure reached in these experiments. At pH 8.0, TYMV remained unaffected by pressure up to 160 MPa, but decapsidated irreversibly above 200 MPa, giving rise to more and more empty shells upon increasing pressure. The organization of these empty shells was similar to that of the capsid of native virions, apart from the presence of a hole corresponding to the loss of a group of 5–8 coat protein subunits, through which the RNA may have escaped. At variance with other small isometric viruses, the capsid of TYMV never dissociated under pressure into subunits or small aggregates of subunits. This exceptional behavior of TYMV is probably due to the importance of van der Waals contacts and hydrogen bonds in the stability of its capsid.