Polymerization of the tubulin-colchicine complex and guanosine 5'-triphosphate hydrolysis

Abstract

The tubulin-colchicine (1:1) complex was able to polymerize in vitro under the buffer conditions of microtubule assembly from pure native tubulin [pig brain]. The physical characteristics of this peculiar polymer were investigated under a variety of conditions and compared with those of microtubules. Polymerization which consisted of nucleation followed by a growth process, was characterized by a critical concentration and exhibited divalent ion, temperature and pH dependences very similar to those of microtubules. GTP or 5''-guanylyl methylenediphosphate (GMPPCP) was required for polymerization, and GDP was a potent inhibitor. GTP hydrolysis was totally disconnected from the polymerization process and occurred as well under nonpolymerizing conditions. The results are discussed in view of the different types of protein-protein interactions exhibited by tubulin and of the possible relationship between the conformation of the GTP site and the interaction areas.