Epothilones electron crystallography

Fig. 11 Three-dimensional structures of epothilones determined in different environments (O red, S yellow, N dark blue). Top structures of free EpoA determined by X-ray crystallography from dichloromethane/petroleum ether (top left [9 8] (a)) and from methanol/water (top right [143](b)). Bottom structures of EpoA bound to tubulin determined by solution NMR in aqueous medium (bottom left [96]) and by electron crystallography from zinc-stabilized tubulin sheets (bottom right [26]).(a) The crystal structure data have been available from the author to interested research groups since October 1995.(b) H.-J. Hecht, G. Hofle, unpublished results CCDC 241333 and CCDC 241334 contain the crystallographic data of this structure. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retiieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK fax (+ 44) 1223-336-033 or deposit cede. cam. ac. uk)...

Keywords Diffraction, Dynamics, Electron crystallography, Epothilone, Lauli-malide, Microtubules, Modeling, Paclitaxel, SAR, Taxol, Tubulin... 

Fig. 18 The solution of epothilone bound to tubulin by electron crystallography, a 2Fo-Fc map and model of epothilone A bound to tubulin at la (ltvk) [3], b Energy optimized model derived from ltvk through MAID protocol used as template for analysis of SAR and design of new analogs...

Based on analysis of electronic crystallography and NMR data for the bindings of Taxol and epothilone A to tubulin subunits, it was proposed that they did not share a common pharmacophore (similar binding mode and sites) as hypothesized for a long time, because they bind to their receptors uniquely and independently. Also, the T-shape conformation of Taxol binding to tubulin was supported from this study. 

Initially, data were collected on crystal structure and conformation of epothilone B in solution [13], together with information on the binding site of epothilone A on a/p-tubulin, using electron crystallography and molecular modelling (Fig. 16.2)... 

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