TUBULIN GTP HYDROLYSIS INFLUENCES THE STRUCTURE, MECHANICAL-PROPERTIES, AND KINESIN DRIVEN TRANSPORT OF MICROTUBULES

Tubulin is a GTPase that hydrolyzes its bound nucleotide triphosphate after it becomes incorporated into a microtubule. The only known conse quence of nucleotide hydrolysis is that it increases the dissociation rate of tubulin from the end of the microtubule by 2 orders of magnitu de. In this study, we investigated whether microtubules composed of tu bulin-GMPCPP (guanylyl alpha,beta-methylenediphosphate) (a very slowly hydrolyzed GTP analog) or tubulin-GDP exhibit additional structural o r functional differences. We show that tubulin-GMPCPP microtubules are significantly stiffer than tubulin-GDP microtubules and have a 21% sh allower protofilament twist angle. We also find that kinesin, a microt ubule-based motor protein, transports tubulin-GMPCPP microtubules at s imilar to 30% faster rates than tubulin-GDP microtubules. These findin gs suggest that growing microtubule ends, which are thought to be comp osed of tubulin-GTP, may have different structural and mechanical prop erties from the remainder of the microtubule polymer.