| This thesis examines the cytoskeletal filaments called microtubules, including three investigations on the binding of the chemotherapeutic drug taxol and one investigation exclusively on the microtubule-associated protein, tau. On the binding of taxol to microtubules, we have modified a method called fluorescence recovery after photobleaching to observe the binding of taxol to microtubules. Using this method, we find that the nucleotide-triphosphate GMPCPP shifts the binding curve by lowering the equilibrium dissociation constant and decreasing the dissociation rate. The protein tau changes the binding of taxol to microtubules by making the binding appear cooperative, with a maximal Hill coefficient of 15. The final investigation employs atomic force microscopy and the surface forces apparatus to measure the forces exerted by three different tau protein isoforms in various solution conditions. We find that the tau has no folded structure by AFM pulling, but that it does display a self-attraction in the surface forces measurements, which is mediated by the N-terminal inserts. |
