The bioactive Taxol conformation on β-tubulin: Experimental evidence from highly active constrained analogs

Abstract

The important anticancer drug Taxol (paclitaxel) binds to tubulin in a stoichiometric ratio and promotes its assembly into microtubules. The conformation of microtubule-bound drug has been the subject of intense study, and various suggestions have been made. In this work we present experimental and theoretical evidence that Taxol adopts a T-shaped conformation when it is bound to tubulin.

Rotational-Echo Double-Resonance NMR Distance Measurements for the Tubulin-Bound Paclitaxel Conformation

“…33 It is no coincidence that virtually every recent synthetic program attempting to prepare more potent and less resistant taxanes based on biostructural principles has employed the EC structure. 18,20,29,37 Furthermore, the tubulin dimer structure derived from Zn +2 -stabilized sheets has been modeled into the 8 Å resolution microtubule structure determined by cryoelectron microscopy 38 and shown to be entirely consistent with the MT structure. Finally, as we have pointed out previously, 17,20,29 not only is the REDOR geometry derived from lyophilized MTs coincident with the T-Taxol form (Table 2), but bioactivities in situations where MTs are present as soluble dynamic entities can be significantly improved by exploiting the EC structure and bound ligand from stabilized tubulin sheets.…”

“…17,19 The T-Taxol conformation has been strongly supported by indirect evidence showing that the synthesis of constrained analogs based on this conformation yields compounds with improved activity. 20 In this paper, we provide data on the synthesis and REDOR NMR analysis of additional PTX analogs which provide further experimental evidence for the T-Taxol conformation.…”

Solid‐state NMR studies of the molecular structure of Taxol

“…16 The T-shaped conformers superimpose well with the binding conformation of Taxol inˇ-tubulin. 17,31 The structural information determined by solution NMR in nonpolar organic solvents 18,19 or mixture of polar and organic solvents 15 have significant differences 20,21 and we are thus motivated to investigate the molecular structure of Taxol in solid phase. In this work, we applied 13 C solid-state NMR spectroscopy to characterize the structure of Taxol in powder form.…”

The paclitaxel site in tubulin probed by site‐directed mutagenesis of Saccharomyces cerevisiae β‐tubulin

“…Several models have been proposed for the conformation of the tubulin bound form of paclitaxel, but evidence appears to support the so-called T-taxol conformation [6,[20][21][22][23]. The original modeling of the T-taxol conformer in the binding site showed close interactions of the CH 2 groups of K19 and D26 and the isopropyl side chain of V23 with the 3 0 -benzamido phenyl ring [6].…”