Question

Microtubule (MT) dynamics in a given cell type can be influenced by the expression of different isoforms of α and β tubulin and/or by various post-translational modifications. Tubulin isoforms or post-translational modifications that would destabilize MTs could do so by:

• A. Increasing α tubulin GTPase activity and/or increasing β tubulin GAP activity
• B. Increasing α tubulin GAP activity and/or increasing β tubulin GTPase activity
• C. Reducing α tubulin GAP and/or reducing β tubulin GTPase activity
• D. Reducing α tubulin GTPase activity and/or increasing β tubulin GAP activity
• E. Reducing β tubulin GTPase activity and/or reducing β tubulin GAP activity

Answer 1

The correct answer would be A

Microtubule polymerization requires a-tubulin/b-tubulin dimer. It is this dimer that polymerizes into microtubule. This polymerization is GTP dependent and both a-tubulin and b-tubulin binds to GTP. They also have GTPase activity. GTP that binds to a-tubulin is neither hydrolyzed nor exchanged as it stuck between a-tubulin/b-tubulin interface. It is the GTP that binds to b-tubulin that regulate polymerization and hydrolysis of GTP to GDP cause depolymerization. b-tubulin also have intrinsic GAP activity that accelerated GTPase activity. So to destabilize the MTs one needs to increase the GTPase activity of both a-, and b-tubulins and GAP activity of b-tubulin.