Interaction of tubulin with non-denaturing amphiphiles

Soluble purified calf brain tubulin contains extensive and easily accessible regions capable of hydrophobic interactions. The binding of non-ionic and mild anionic detergents to this protein has been characterized by difference absorption spectroscopy and equilibrium gel chromatography with labelled ligands. Tubulin bound reversibly and co-operatively 0.42 +/- 0.05 g deoxycholate per g protein and bound octyl glucoside at a minimal stoichiometry of 0.26 g per g protein. Binding of deoxycholate and octyl glucoside perturbed the protein absorption, quenched the fluorescence, and produced a moderate change in the far u.v. circular dichroism of tubulin. These changes have been interpreted as the result of detergent binding near aromatic amino acids and the production of a structural change different from detergent-induced denaturation. Deoxycholate and octyl glucoside inhibited colchicine binding. Octyl glucoside and Triton X-100 inhibited the in vitro self-assembly of tubulin into microtubules, whereas small concentrations of deoxycholate were found to enhance microtubule formation.