Balaguer, Francisco de AsísMühlethaler, TobiasEstévez-Gallego, JuanCalvo, EnriqueGiménez-Abián, Juan FranciscoRisinger, April LSorensen, Erik JVanderwal, Christopher DAltmann, Karl-HeinzMooberry, Susan LSteinmetz, Michel OOliva, María ÁngelaProta, Andrea EDíaz, J Fernando2019-04-262019-04-262019-03-20Int J Mol Sci. 2019; 20(6):E13921422-0067http://hdl.handle.net/20.500.12105/7516It 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.engVoRCyclostreptinMicrotubulesMultidrug resistanceTaxanesTubulinAtribución 4.0 Internacional30897704206139210.3390/ijms200613921422-0067International journal of molecular sciencesopen access