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Crystal Structure of the Cyclostreptin-Tubulin Adduct: Implications for Tubulin Activation by Taxane-Site Ligands.

Francisco de Asís BalaguerTobias MühlethalerJuan Estévez-GallegoEnrique CalvoJuan Francisco Giménez-AbiánApril L RisingerErik J SorensenChristopher D VanderwalKarl-Heinz AltmannSusan L MooberryMichel O SteinmetzMaría Ángela OlivaAndrea E ProtaJosé Fernando Díaz
Published in: International journal of molecular sciences (2019)
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.
Keyphrases
  • metastatic breast cancer
  • transcription factor
  • induced apoptosis
  • cell cycle arrest
  • cell proliferation
  • cell death
  • molecular dynamics simulations