Abstracts

Cellular membranes constantlyexperience remodeling, as exemplified by morphological changesduring endo- and exocytosis. Regulation of membrane morphology isessential for these processes. In this work, we attempt toestablish a regulation path based on the use of photoswitchesexhibiting conformational changes in model membranes, namely, giantunilamellar vesicles (GUVs). The mechanism of the changes in theGUVs morphology caused by isomerization of the photosensitivemolecules has been previously explored but still remains elusive.We examine the morphological reshaping of GUVs in the presence ofthe photoswitch o-tetrafluoroazobenzene (F-azo) and show that themechanism behind the resulting morphological changes involves bothan increase in the membrane area and generation of a positivespontaneous curvature. First, we characterize the partitioning ofF-azo in a single-component membrane using both experimental andcomputational approaches. The partition coefficient calculated frommolecular dynamic simulations agrees with experimental dataobtained with size-exclusion chromatography. Then, we implement theapproach of vesicle electrodeformation in order to assess theincrease in the membrane area, which is observed as a result of theconformational change of F-azo. Finally, the local and theeffective membrane spontaneous curvatures were estimated from theobserved shapes of vesicles exhibiting outward budding. We thenextend the application of the F-azo to multicomponent lipidmembranes, which exhibit a coexistence of domains in differentliquid phases due to a miscibility gap between the lipids. Weperform initial experiments to investigate whether F-azo can beemployed to modulate the lateral lipid packing and organization. Weobserve either complete mixing of the domains or the appearing ofdisordered domains within the domains of more ordered phase. Thetype of behavior observed in response to the photoisomerization ofF-azo was dependent on the used lipid composition. We believe thatthe findings introduced here will have an impact in understandingand controlling both lipid phase modulation and regulation of themembrane morphology in membrane systems. Zellulre Membranen durchlaufenstndige Formvernderungen wie zum Beispiel bei der Endo- undExozytose. Fr diese und andere Prozesse ist eine Regulierung derMembranmorphologie notwendig. In der vorliegenden Arbeit wurdenriesen unilamellare Vesikel (giant unilamellar vesicles, GUVs) alsModelmembranen genutzt. nderungen der Vesikelform wurde durchlichtschaltbare Molekle (Fotoschalter) erzielt. Dass dieIsomerisierung von lichtempfindlichen Moleklen eine Verformung vonGUV ermglichen kann, war bekannt. Jedoch war der zugrunde liegendeMechanismus unklar. In dieser Arbeit wurde zur Untersuchung diesesMechanismus o-Tetrafluoroazobenzol (F-azo) als Fotoschalterverwendet. Damit konnte gezeigt werden, dass sowohl eineVergrerung der Membranflche als auch das Entstehen einerpositiven, spontanen Membrankrmmung den morphologischenVernderungenAdvisors/Committee Members: Dimova, Rumiana (advisor).