Adhesion and Fusion of Model Lipid Membranes

• Applicant: Privatdozentin Dr. Rumiana Dimova
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2004 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5415789

Adhesion and fusion of membranes is essential for cellular processes like compartmentalization, import of foodstuffs and export of waste (exo- and endocytosis), reproduction, and cell division. Usually, these processes involve participation of proteins. Yet, little is known about the molecular mechanisms by which fusion occurs. An appealing approach to study membrane fusion is to characterize the conditions and events necessary for adhesion and fusion of simple purely lipid membranes and then to infer what vital functions can be attributed to fusogenic agents. Our main interest will be directed towards studying and understanding the action of synthesized ('artificial') fusogenic molecules which are important especially for targeted drug delivery. Adhesion/fusion studies have been performed on various systems, most commonly vesicle - planar bilayer and vesicle - vesicle. The steps occurring in these processes can be characterized in several ways. Fluorescent techniques are the most often involved in quantification of adhesion and fusion. Static techniques like freeze fracture electron microscopy are also employed using small unilamellar vesicles. Another interesting and relatively new approach for assessing the degree of interaction is Isothermal Titration Calorimetry (ITC). ITC uses admixing of adhesion/fusion inducing agent to solution of lipid vesicles (of approximately 100 nm size) will induce vesicle-agent and/or vesicle-vesicle interaction. This can be considered as a "reaction" with corresponding enthalpy and equilibrium constant. The dynamics of vesicle stability before and after the interaction can be followed by Dynamic Light Scattering and fluorimetry in case of a fluorescent probe present in the membranes. The events during adhesion/fusion can be directly observed on a microscopic level when working with giant vesicles (several tens of microns in diameter). Two vesicles can be brought together with micropipettes or via optical trap manipulation and the adhesion zone between the vesicles can be visualized. The contact angle between the membranes is a measure for the adhesion energy. Performing measurements at different aspiration pressures will provide knowledge about the membrane tension necessary for adhesion/fusion.

• DFG Programme: Research Grants
• International Connection: France
• Participating Persons: Professor Dr. Reinhard Lipowsky; Dr. Valérie Marchi-Artzner