The lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape... Show moreThe lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape of the membrane. This two-way interaction gives rise to a force between membrane-deforming objects that is mediated by the membrane. In this thesis, this effect is measured by employing micron-sized colloidal particles. In Chapters 2 and 3, methods for extracting local forces from video images of colloidal particles are described. Then, in Chapter 4, the development of colloidal particles that strongly attach to specific lipid membranes is described. These are then used in Chapters 5 and 6, in which membrane-mediated forces and assembly pathways between membrane-attached colloidal particles are investigated and quantified. Finally, in Chapters 7 and 8, the preparation of micron-sized oil droplets is studied and their use as lipid monolayer support is demonstrated. The results from this thesis contribute to fundamental microbiological questions about forces between membrane proteins, as well as to the understanding of the toxicity of microplastics. Show less
Membrane tubes are ubiquitous within cells. They have a diameter of approximately 50 nanometers, and are formed when a sufficiently large localized force is exerted on a membrane. Important... Show moreMembrane tubes are ubiquitous within cells. They have a diameter of approximately 50 nanometers, and are formed when a sufficiently large localized force is exerted on a membrane. Important generators of this force are the motor proteins that can move along cytoskeletal filaments. We studied membrane tube formation by motor proteins from giant vesicles in an in vitro reconstituted system, and showed that motor proteins can dynamically associate to form clusters that work together. In addition, the physical parameters that determine the force required to form tubes were examined, and it was found that the force barrier for tube formation increases with the area the pulling force is exerted on. Finally, some first results are presented on the competition between motor proteins of opposite directionality. Our findings suggest regulatory mechanisms that may be used for the intracellular spatial organization of membranes. Show less
