Differential effects of colchicine and its B-ring modified analog MTPT on the assembly-independent GTPase activity of purified beta-tubulin isoforms from bovine brain

Tubulin occurs as several isoforms whose physiological significance is not clear, The binding of colchicine to tublelin inhibits its assembly and is associated with a stimulation of the intrinsic GTPase activity of tubulin. In an effort to study the conformational states of different beta-tubulin isoforms in the drug-bound form, the intrinsic CTPase activity was studied in the presence of colchicine and its B-ring-modified analog MTPT. The results show that the GTPase activities of alpha beta(II), alpha beta(III) and alpha beta(IV), are 3.1, 2.8, and 2.6 nmole/h/ml. In the presence of colchicine, the values were increased to 4.5, 9.6, and 3 nmole/h/ml for alpha beta(II), alpha beta(III) and alpha beta(IV) respectively. In the case of MTPT, which lacks the B-ring, the GTPase activities were 5.8, 11.5, and 7.3 nmole/h/ml, respectively, for alpha beta(II), alpha beta(III), and alpha beta(IV) The results show that the B-ring of colchicine contributes differentially to the conformational changes in the beta-tubulin isoforms. (C) 1997 Academic Press.