Molecular dynamics simulation and density functional theory studies on the active pocket for the binding of paclitaxel to tubulin.

Paclitaxel (PTX) is used to treat various cancers, but it also causes serious side effects and resistance. To better design similar compounds with less toxicity and more activity against drug-resistant tumors, it is important to clearly understand the PTX-binding pocket formed by the key residues of active sites on β-tubulin. Using a docking method, molecular dynamics (MD) simulation and density functional theory (DFT), we identified some residues (such as Arg278, Asp26, Asp226, Glu22, Glu27, His229, Arg369, Lys218, Ser277 and Thr276) on β-tubulin that are the active sites responsible for interaction with PTX. Another two residues, Leu371 and Gly279, also likely serve as active sites. Most of these sites contact with the "southern hemisphere" of PTX; only one key residue interacts with the "northern hemisphere" of PTX. These key residues can be divided into four groups, which serve as active compositions in the formation of an active pocket for PTX binding to β-tubulin. This active binding pocket enables a very strong interaction (the strength is predicted to be in the range of -327.8 to -365.7 kJ mol(-1)) between β-tubulin and PTX, with various orientated conformations. This strong interaction means that PTX possesses a high level of activity against cancer cells, a result that is in good agreement with the clinical mechanism of PTX. The described PTX pocket and key active residues will be applied to probe the mechanism of tumor cells resistant to PTX, and to design novel analogs with superior properties.