Magnesium-induced structural changes in tubulin.

Exogenously added Mg2+, in the intracellular concentration range, has significant effect on the conformation of tubulin as monitored by tryptophan fluorescence. This magnesium-induced conformational change is reflected in the change of the slope and intercept of the Lehrer plot. The off-rate of colchicine from colchicine-tubulin complex is also decreased severalfold upon the addition of exogenous magnesium. The conformational change is magnesium-specific, and magnesium can only be replaced by manganese. GTP, CaCl2, and NaCl have no effect. Magnesium, however has no effect on tryptophan accessibilities of tubulin-S. Implications of these results are discussed in terms of C-terminal tail-body interaction.