Evaluation of the tubulin-bound paclitaxel conformation:: Synthesis, biology, and SAR studies of C-4 to C-3′ bridged paclitaxel analogues

The important anticancer drug paclitaxel binds to the beta-subunit of the alpha beta-tubulin dimer in the microtubule in a stoichiometric ratio, promoting microtubule polymerization and stability. The conformation of microtubule-bound drug has been the subject of intense study, and various suggestions have been proposed. In previous work we presented experimental and theoretical evidence that paclitaxel adopts a T-shaped conformation when it is bound to tubulin. In this study we report additional experimental data and calculations that delineate the allowable parameters for effective paclitaxel-tubulin interactions.