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The subject of this PhD thesis concerns a protein belonging to the enzymatic catalysis : the bovine pancreatic trypsin inhibitor or BPTI which is a model system much studied by several techniques but less by neutron scattering. It is a small protein ( 58 amino acid residues, a molecular weight of 6500 Da) which has a very high stability since it cannot be denatured at temperatures below 95°C or at pressures below 14 kbar. This stability is due to the presence of three disulphide bridges and three salt bridges. We have studied the structure and the dynamics of native state and thermal and pressure denatured states of BPTI by neutron scattering technique. By small angle neutron scattering we have observed an increase of the radius of gyration of the protein in solution at 95°C and a reduction of this radius under 6000 bar. The ellipsoidal shape of the molecule in the native state do not change between 22°C and 95°C but we have observed an increase of the volume of BPTI. Indeed, the shape of BPTI is modified from an ellipsoidal one to a spherical one at 3000 bar, while it is well represented by a micelle when applied pressure values reach 5000 and 6000 bar.Further experiments by infrared spectroscopy and by UV-visible spectroscopy as a function of temperature and pressure allowed us to confirm our results. Quasielastic neutron scattering allowed us to observe an opposite effect of temperature and pressure on global motions and internal dynamics of BPTI in solution. Increasing temperature induces a faster dynamics of these global and internal Motions whereas increasing pressure induces a slowing down of these motions.; Ce travail de thèse porte sur une protéine de la catalyse enzymatique : l'inhibiteur de la trypsine pancréatique bovine ou BPTI qui est un système modèle très étudié par différentes techniques mais peu par diffusion de neutrons. Il s'agit d'une petite protéine (58 résidus d'acides aminés, poids moléculaire de 6500 Da) qui possède une très grande stabilité puisqu'elle ne peut être dénaturée à des température inférieures à 95°C ou à des pressions inférieures à 14 kbar. Cette stabilité est due à la présence de trois ponts disulfures et de trois ponts salins. Nous avons étudié la structure et la dynamique de l'état natif et des états dénaturés par la température et par la pression, du BPTI, par la technique de diffusion de neutrons. La diffusion de neutrons aux petits angles nous a permis d'observer une augmentation du rayon de giration de la protéine en solution à 95°C et une réduction de ce rayon à 6000 bar. La forme ellipsoïdale de la molécule à l'état natif n'est pas modifiée entre 22°C et 95°C mais présente une augmentation du volume du BPTI. De plus, la forme du BPTI est modifiée depuis une forme ellipsoïdale dans l'état natif, vers une forme globulaire à 3000 bar et micellaire lorsque la pression atteint 5000 et 6000 bar. Des expériences complémentaires par spectroscopie infrarouge et UV-visible, en température et en pression, ont permis de confirmer ces résultats. La diffusion quasiélastique de neutrons a permis d'observer un effet antagoniste de la température et de la pression sur les mouvements globaux et sur la dynamique interne du BPTI en solution. L'augmentation de la température a pour effet d'induire des mouvements globaux et internes plus rapides tandis que l'augmentation de la pression induit un ralentissement de ces mouvements.

Biophysical journal 114(1), 146 - 157 (2018). doi:10.1016/j.bpj.2017.11.009, We measured the effect of intrinsic lipid curvature,$J_{0}$ , on structural properties of asymmetric vesicles made of palmitoyl-oleoyl-phosphatidylethanolamine (POPE; $J_{0} < 0$) and palmitoyl-oleoyl-phosphatidylcholine (POPC;$J_{0} \sim 0$). Electron microscopy and dynamic light scattering were used to determine vesicle size and morphology, and x-ray and neutron scattering, combined with calorimetric experiments and solution NMR, yielded insights into leaflet-specific lipid packing and melting processes. Below the lipid melting temperature we observed strong interleaflet coupling in asymmetric vesicles with POPE inner bilayer leaflets and outer leaflets enriched in POPC. This lipid arrangement manifested itself by lipids melting cooperatively in both leaflets, and a rearrangement of lipid packing in both monolayers. On the other hand, no coupling was observed in vesicles with POPC inner bilayer leaflets and outer leaflets enriched in POPE. In this case, the leaflets melted independently and did not affect each other’s acyl chain packing. Furthermore, we found no evidence for transbilayer structural coupling above the melting temperature of either sample preparation. Our results are consistent with the energetically preferred location of POPE residing in the inner leaflet, where it also resides in natural membranes, most likely causing the coupling of both leaflets. The loss of this coupling in the fluid bilayers is most likely the result of entropic contributions., Published by Elsevier, Bethesda, Md.

Sulfavant A (1) and Sulfavant R (2) are amphiphilic sulfoquinovoside-glycerol lipids under study as molecular adjuvants of vaccines. Their structures differ only for the configuration of the oxymethine carbon of glycerol that is R/S in 1 and R in 2. The in vitro activity of both products follows a bell-shaped dose-response curve but 1 gave the best response between 10 and 30 µM, while 2 was active at 10 nM. Characterization of aqueous self-assembly of these molecules by a multi-technique approach based on surface tensiometry, dynamic light scattering (DLS), nuclear magnetic resonance (NMR), fluorescence light phase contrast, and cryo-electron microscopy has finally clarified this divergent and controversial biological outcome. The study proved the occurrence of supramolecular structures at concentrations much lower than the critical aggregation concentration (CAC) calculated by surface tensiometry for both products. The shape and size of these aggregates varied as a function of the concentrations differently for 1 and 2. At nanomolar concentration, Sulfavant A (1) formed cohesive vesicular structures, while Sulfavant R (2) arranged in small spherical micellar particles whose reduced stability was responsible for an increase of the monomer concentration that well agreed with the immunomodulatory activity. On the other side, micromolar concentrations led to an increase of particle sizes of both compounds and a transition from micellar to the vesicular state of Sulfavant R (2). The thermodynamic stability of these aggregates correlated with the activity of 1 above 10 µM and the complete loss of efficacy of 2 at micromolar concentrations. The study of Sulfavants provides clear evidence of how self-aggregation and thus the equilibria between the monomers and the supramolecular forms of lipophilic products in aqueous media determine the overall response of these substances in cell-based assays.

The safe application of nanotechnology devices in biomedicine requires fundamental understanding on how they interact with and affect the different components of biological systems. In this respect, the cellular membrane, the cell envelope, certainly represents an important target or barrier for nanosystems. Here we report on the interaction between functionalized SuperParamagnetic Iron Oxide Nanoparticles (SPIONs), promising contrast agents for Magnetic Resonance Imaging (MRI), and lipid bilayers that mimic the plasma membrane. Neutron Reflectometry, supported by Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) experiments, was used to characterize this interaction by varying both SPION coating and lipid bilayer composition. In particular, the interaction of two different SPIONs, functionalized with a cationic surfactant and a zwitterionic phospholipid, and lipid bilayers, containing different amount of cholesterol, were compared. The obtained results were further validated by Dynamic Light Scattering (DLS) measurements and Cryogenic Transmission Electron Microscopy (Cryo-TEM) images. None of the investigated functionalized SPIONs were found to disrupt the lipid membrane. However, in all case we observed the attachment of the functionalized SPIONs onto the surface of the bilayers, which was affected by the bilayer rigidity, i.e. the cholesterol concentration.

Hydrophobins are fungal proteins whose functions are mainly based on their capability to self-assemble into amphiphilic films at hydrophobic-hydrophilic interfaces (HHI). It is widely accepted that class I hydrophobins form amyloid-like structures, named rodlets, which are hundreds of nanometers long, packed into ordered lateral assemblies and do not exhibit an overall helical structure. We studied the self-assembly of the Class I hydrophobin Vmh2 from Pleurotus ostreatus in aqueous solutions by dynamic light scattering (DLS), thioflavin T (ThT), fluorescence assay, circular dichroism (CD), cryogenic trasmission electron microscopy (cryo-TEM), and TEM. Vmh2 does not form fibrillar aggregates at HHI. It exhibits spherical and fibrillar assemblies whose ratio depends on the protein concentration when freshly solubilized at pH ≥ 7. Moreover, it spontaneously self-assembles into isolated, micrometer long, and twisted amyloid fibrils, observed for the first time in fungal hydrophobins. This process is promoted by acidic pH, temperature, and Ca(2+) ions. A model of self-assembly into amyloid-like structures has been proposed.

Liposomes are complex aggregates, often including polyethylene glycol (PEG) to expand their life span in vivo, although their full biocompatibility is still questioned. With the aim to suitably replace PEG within liposomal formulations, here we propose a new liposomes formulation, which includes an amphiphilic molecule of natural origin: the lipooligosaccharide (LOS) from the Gram-negative bacterium Rhizobium rubi. LOS architecture is bifunctional: the lipid moiety at one terminus promotes its insertion into the liposome, the other terminus is hydrophilic and in this case presents an oligosaccharide motif similar to the human Lewis B antigen. Liposomes were prepared by co-formulating de-O-acylated LOS (de-LOS) with the lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and the anticancer nucleolipid-based Ru(III) complex, ToThyRu. In-depth microstructural characterization shows that de-LOS containing liposomes are stable aggregates. In vitro preliminary bioscreens have disclosed their negligible toxic profile and a good uptake in MCF-7 and HaCaT cells. The results validate the use of lipooligosaccharides in formulating liposomes and pave the way to their use in drug delivery applications.