The binding conformation of Taxol in β-tubulin: A model based on electron crystallographic density
- †Department of Chemistry, Emory University, Atlanta, GA 30322; ‡Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and §Molecular and Cell Biology, University of California, Berkeley, CA 94720
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Edited by Aaron Klug, Medical Research Council, Cambridge, United Kingdom, and approved December 19, 2000 (received for review July 3, 2000)
Abstract
The chemotherapeutic drug Taxol is known to interact within a specific site on β-tubulin. Although the general location of the site has been defined by photoaffinity labeling and electron crystallography, the original data were insufficient to make an absolute determination of the bound conformation. We have now correlated the crystallographic density with analysis of Taxol conformations and have found the unique solution to be a T-shaped Taxol structure. This T-shaped or butterfly structure is optimized within the β-tubulin site and exhibits functional similarity to a portion of the B9-B10 loop in the α-tubulin subunit. The model provides structural rationalization for a sizeable body of Taxol structure–activity relationship data, including binding affinity, photoaffinity labeling, and acquired mutation in human cancer cells.
Footnotes
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↵ * To whom reprint requests should be addressed. E-mail: snyder{at}euch4e.chem.emory.edu.
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This paper was submitted directly (Track II) to the PNAS office.
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↵ ¶ The structure of the αβ-tubulin dimer refined to 3.5 Å was obtained by using simulated annealing torsion angle refinement and phase information from experimental images; R factor 0.23 and free R factor 0.30; J. Lowe., T. Li, K.H.D., and E.N., unpublished data.
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↵ ‖ A protofilament consists of a longitudinal head-to-tail stacking of αβ-tubulin dimers. These extended and observable macrostructures are capable of assembling laterally to give cylindrical MTs; see ref. 36.
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↵ ** The EC structure determination used wild-type pig-brain tubulin with β-Ser. Formally, the β-Ala-364→Thr mutation is β-Ser-364→Thr here.
- Abbreviations:
- MT,
- microtubule;
- TB,
- tubulin;
- EC,
- electron crystallography;
- PTX,
- paclitaxel
- Copyright © 2001, The National Academy of Sciences
