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Cyclostreptin and Microtubules: Is a Low‐Affinity Binding Site Required?
Author(s) -
Prussia Andrew J.,
Yang Yutao,
Geballe Matthew T.,
Snyder James P.
Publication year - 2010
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200900538
Subject(s) - microtubule , tubulin , binding site , biophysics , chemistry , dimer , taxane , stereochemistry , ligand (biochemistry) , biochemistry , biology , microbiology and biotechnology , receptor , genetics , organic chemistry , cancer , breast cancer
Cyclostreptin (CS) is a recently discovered natural product with cytotoxic activity caused by microtubule stabilization. It is the only known microtubule‐stabilizing agent (MSA) that covalently binds to tubulin. It also exhibits the fast‐binding kinetics seen for other MSAs. Through careful peptide digestion and mass spectrometry analysis, Buey et al. found that two amino acids are labeled by CS: Asn228, near the known taxane‐binding site, and Thr220, in the type I microtubule pore. This led Buey et al. to propose Thr220 resides at the site previously predicted to be a way station or low‐affinity site. By using molecular dynamics simulations and structural considerations of the microtubule pore and tubulin dimer, we conclude that postulation of a low‐affinity site is unnecessary to explain the available experimental data. An alternative explanation views the microtubule pore as a structural entity that presents a substantial kinetic barrier to ligand passage to the known taxane‐binding site—an entry point to the microtubule lumen that becomes completely blocked if cyclostreptin is bound at Thr220. Simulations of the free dimer also suggest a common mechanism of microtubule stabilization for taxane site MSAs through their conformational effect on the M‐loop. Such an effect explains the low tubulin polymerization caused by cyclostreptin in vitro despite its covalent attachment.