Physical study on the bio self-assembled nanotube under the influence of stabilizing agents

Abstract

This dissertation work focus upon the microtubule (MT), which is a bio self-assembled cytoskeletial filamentous protein as a model system of nanotube. However, the MT is a hollow tube and its interior is arguably small that a functional relevance is little known of how or why proteins or drugs interact with microtubule lumen. Here, we use fluorescence after photobleaching (FRAP) to study the binding and re-binding of the anti-cancer drug taxol to a site known to lie on the interior of the microtubule, and how it is affected by microtubule-associated protein Tau. Through FRAP measurements on a fluorescently labeled taxol on MT decorated with different tau isoforms, we discovered that Tau commonly induces taxol to bind MT cooperatively. But one of Tau isoform speeds up the rate of taxol passage through the pores on the MT wall. To understand Tau effects on taxol, quantitative modeling for mobility based on the taxol kinetics was presented and it allowed an estimation of cooperativity and mechanisms for the fast mobility. In light of these results, we discuss the extent to which these two biologically distinct ligands either compete or collaborate to facilitate escape and what the isoform effect implies about the biological functions of Tau and the MT interior. As second topic, we study the microtubule growth inside confined space in the presence of stabilizing agent. We create the cell-sized vesicle made of lipids bilayer in vitro as a good model system of a living cell. In experimentally, we archive the evolution of vesicle containing of microtubule under the influence of taxol using optical microscopy. We reveal that the hydrophobic stabilizer, taxol, crosses the membrane and binds to MTs. It also stimulates polymerization of MT with fast growth rate and interrupts MTs bundling. Most surprising result is that MTs place just underneath of the membrane and make sharp edge despite of energetical unfavorable position. To understand what determined this shape e...