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Tubulin Rings

We are investigating the assembly and disassembly conditions for single tubulin rings and their relation to microtubule (MT) assembly and disassembly kinetics. We have determined the structure of single GDP-rich tubulin rings using cryo-TEM (in collaboration with Dr. Yael Levi-Kalisman)  and synchrotron solution X-ray scattering. The scattering curves were fitted to atomic models or tubulin single rings, using our analysis software D+.

tubulin rings
Tubulin single rings form above a critical tubulin concentration. The rings dissociate upon addition of GTP, or by increasing the temperature, or by exposure to the X-ray beam.

 

We found that there is a critical concentration for ring formation, which increases with GTP concentration or with temperature. We have also found that during MT assembly, the fraction of rings and unassembled tubulin dimers simultaneously decreases. During MT disassembly, however, the mass fraction of dimers increases but the increase in the concentration of rings is delayed until the fraction of dimers is sufficiently high. Interestingly, X-ray radiation can trigger tubulin ring disassembly, and the disassembly reaction follows first-order kinetics (Biochemistry 2018).