The B‐ring substituent at C‐7 of colchicine and the α‐C‐terminus of tubulin communicate through the “tail–body” interaction

Abstract

The carboxy terminals of alphabeta-tubulins are flexible regions rich in acidic amino acid residues that play an inhibitory role in the polymerization of tubulin to microtubules. We have shown that the binding of colchicine and its B-ring analogs (with C-7 substituents) to tubulin are pH sensitive and have high activation energies. Under identical conditions, the binding of analogs without C-7 substituents is pH independent and has lower activation energy. Beta-C-terminus-truncated tubulin (alphabeta(s)) shows similar pH sensitivity and activation energy to native tubulin (alphabeta). Removal of the C-termini of both subunits of tubulin (alpha(s)beta(s)) or the binding of a basic peptide P2 to the negatively charged alpha-C-terminus of tubulin causes a colchicine-tubulin interaction independent of pH with a low activation energy. Tubulin dimer structure shows that the C-terminal alpha-tail is too far from the colchicine binding site to interact directly with the bound colchicine. Therefore, it is likely that the interaction of the alpha-C-terminus with the main body of tubulin indirectly affects the colchicine-tubulin interaction via conformational changes in the main body. We therefore conclude that in the presence of tail-body interaction, a B-ring substituent makes contact with the alpha-tubulin and induces significant conformational changes in alpha-tubulin.

Anti‐mitotic activity of colchicine and the structural basis for its interaction with tubulin

“…68 The activation energies of colchicine binding with P2 peptide-bound tubulin and MTP are 13.89 kcal/mole and 13.58 kcal/mole respectively (Table III). 64 The presence of NaCl lowers the activation energy to 12.68 kcal /mole (Table III). 64 …”

“…The pH sensitivity of other B-ring analogs of colchicine such as deacetylcolchicine (NH 2 Á DAAC), colcemid (NHCH 3 Á DAAC), and N-methylcolcemid (N(CH 3 ) 2 Á DAAC) was tested using quenching of the tryptophan fluorescence of tubulin since it is known that these B-ring analogs fluoresce poorly upon binding to tubulin. 64 Like colchicine, pH-sensitive binding (optimum near pH 7.0) of deacetylcolchicine (NH 2 Á DAAC), colcemid (NHCH 3 Á DAAC), and N-methylcolcemid (N(CH 3 ) 2 Á DAAC) to tubulin was observed. 64 Therefore, on the basis of the above results, it appeared that the negatively charged C-terminus of a-tubulin is involved in a long distance conformational change when a colchicine analog with B-ring side chain at C-7 position binds tubulin.…”

“…64 Like colchicine, pH-sensitive binding (optimum near pH 7.0) of deacetylcolchicine (NH 2 Á DAAC), colcemid (NHCH 3 Á DAAC), and N-methylcolcemid (N(CH 3 ) 2 Á DAAC) to tubulin was observed. 64 Therefore, on the basis of the above results, it appeared that the negatively charged C-terminus of a-tubulin is involved in a long distance conformational change when a colchicine analog with B-ring side chain at C-7 position binds tubulin.…”

“…While the removal of the C-terminus of both subunits (a s b s ) lowers the activation energy significantly to 10.68 kcal/mole, hybrid tubulin (ab s ) (where the C-terminus of only b-tubulin is cleaved) has a high activation energy level of 19.58 kcal /mole. 64 The dissociation of subunits of tubulin (a þ b) also lowers the activation energy to 13.09 kcal /mole. 68 The activation energies of colchicine binding with P2 peptide-bound tubulin and MTP are 13.89 kcal/mole and 13.58 kcal/mole respectively (Table III).…”

Colchicine treatment reversibly blocks cytokinesis but not mitosis in Trypanosoma cruzi epimastigotes

“…The effect of colchicine is the result of its binding to tubulin subunits and the subsequent disruption of the microtubule dynamics (Chakraborty et al 2004). Besides its remarkably toxic and adverse effects, colchicine has been used widely for the treatment of Gout, Familial Mediterranean Fever, and other inflammatory diseases (Cocco et al 2010).…”