Rotational-echo double-resonance NMR distance measurements for the tubulin-bound Paclitaxel conformation.

The important anticancer drug Taxol (paclitaxel, PTX) owes its unique activity to its ability to bind to tubulin in a stoichiometric ratio and promote its assembly into microtubules. The conformation of the microtubule-bound drug has been the focus of numerous research efforts, since the inability of polymerized tubulin to form crystals precludes structure proof by X-ray crystallography. Likewise, although the alpha,beta-tubulin dimer structure has been solved by electron crystallography, the 3.7 A resolution is too low to permit direct determination of either ligand conformation or binding pose. In this article, we present experimental results from H-2{F-19} REDOR NMR that provide direct confirmation that paclitaxel adopts a T-shaped conformation when it is bound to tubulin.