Please use this identifier to cite or link to this item:http://hdl.handle.net/20.500.12105/7516
Crystal Structure of the Cyclostreptin-Tubulin Adduct: Implications for Tubulin Activation by Taxane-Site Ligands
Balaguer, Francisco de Asís | Mühlethaler, Tobias | Estévez-Gallego, Juan | Calvo, Enrique CNIC | Giménez-Abián, Juan Francisco | Risinger, April L | Sorensen, Erik J | Vanderwal, Christopher D | Altmann, Karl-Heinz | Mooberry, Susan L | Steinmetz, Michel O | Oliva, María Ángela | Prota, Andrea E | Díaz, J Fernando
Int J Mol Sci. 2019; 20(6):E1392
It has been proposed that one of the mechanisms of taxane-site ligand-mediated tubulin activation is modulation of the structure of a switch element (the M-loop) from a disordered form in dimeric tubulin to a folded helical structure in microtubules. Here, we used covalent taxane-site ligands, including cyclostreptin, to gain further insight into this mechanism. The crystal structure of cyclostreptin-bound tubulin reveals covalent binding to βHis229, but no stabilization of the M-loop. The capacity of cyclostreptin to induce microtubule assembly compared to other covalent taxane-site agents demonstrates that the induction of tubulin assembly is not strictly dependent on M-loop stabilization. We further demonstrate that most covalent taxane-site ligands are able to partially overcome drug resistance mediated by βIII-tubulin (βIII) overexpression in HeLa cells, and compare their activities to pironetin, an interfacial covalent inhibitor of tubulin assembly that displays invariant growth inhibition in these cells. Our findings suggest a relationship between a diminished interaction of taxane-site ligands with βIII-tubulin and βIII tubulin-mediated drug resistance. This supports the idea that overexpression of βIII increases microtubule dynamicity by counteracting the enhanced microtubule stability promoted by covalent taxane-site binding ligands.