Isolation and structural characterization of natural deuterated lipids and oils from microorganisms

Orateur : Soutenance de Thèse de Robin DELHOM

The formation and structural investigation of planar bilayers from synthetic lipids and natural extracts is described in this thesis. The bilayers were used as model membrane systems for the investigation and quantification of the molecular mechanisms of the membrane-binding antifungal drug Amphotericin B, primarily by neutron reflectometry. Different membrane models of increasing complexity were investigated, with ergosterol or cholesterol included to mimic fungal and mammalian cell membranes, respectively. The extraction, chemical analysis and preparation of hydrogenous and deuterated lipid mixtures from yeasts are presented together with the optimization of the deposition process of supported lipid bilayers on silicon substrates using Quartz Crystal Microbalance with Dissipation monitoring to create relevant natural model membranes for neutron scattering experiments. The effects of deuteration on the lipid composition in two different yeasts, the methylotrophic Pichia pastoris and the pathogenic Candida glabrata are detailed and is shown to be useful for understanding the modulation of the lipids accessible from these microorganisms. Model membranes from the synthetic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine were initially characterized and compared to those formed by the phospholipids or the total lipids extracted from the yeasts, mainly using neutron reflectometry but also membrane diffraction. Finally, the relationship between the lipid composition and the response to Amphotericin B was investigated. Although different behavior of the drug is observed in fungal and mammal membrane mimics, the composition and degree of complexity of the model systems employed were shown to affect the findings and the interpretation of the mechanisms involved in the interaction of the drug with the membranes. The differences found between synthetic and natural lipid systems demonstrate the relevance of the newly developed model membranes from lipids extracted from biomass.

Télécharger dans mon agenda