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The multiple phosphorylation of the microtubule-associated protein MAP2 controls the MAP2:tubulin interaction
Abstract:
Pre-phosphorylation of the microtubule-associated protein MAP2 with the co-purifying cAMP-independent protein kinase (a) decrease the affinity of MAP2 for taxol-stabilised microtubules, (b) increases the dissociation rate constant for microtubule polymerisation, each of which is dependent upon the level of phosphorylation, but (c) has no effect on the association rate constant. Microtubule assembly has no effect on the kinetics of phosphorylation, whereas phosphorylation of pre-assembled microtubules causes their immediate depolymerisation at a rate which is proportional to the initial rate of phosphorylation. The results suggest that the modulated phosphorylation of MAP2 may regulate microtubule length in vivo.
Insights
Pre-phosphorylation of microtubule-associated protein MAP2 by a kinase reduces its binding to microtubules and increases microtubule depolymerization. This suggests phosphorylation regulates microtubule length in vivo.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Microtubules are essential cytoskeletal components involved in cell structure and division.
- Microtubule-associated protein MAP2 plays a crucial role in microtubule stability and dynamics.
- Protein phosphorylation is a key regulatory mechanism in cellular processes.
Purpose of the Study:
- To investigate the effect of MAP2 phosphorylation on its interaction with microtubules.
- To determine how MAP2 phosphorylation influences microtubule polymerization and depolymerization kinetics.
- To explore the potential role of MAP2 phosphorylation in regulating microtubule length in vivo.
Main Methods:
- In vitro assays measuring MAP2 binding affinity to taxol-stabilized microtubules.
- Kinetic analysis of microtubule polymerization and depolymerization rates.
- Phosphorylation of MAP2 using a co-purifying cAMP-independent protein kinase.
- Monitoring microtubule assembly and depolymerization in response to MAP2 phosphorylation.
Main Results:
- Pre-phosphorylation of MAP2 decreased its affinity for microtubules in a phosphorylation-dependent manner.
- Phosphorylation increased the dissociation rate constant of microtubule polymerization but not the association rate constant.
- Phosphorylation of pre-assembled microtubules induced immediate depolymerization, proportional to the phosphorylation rate.
- Microtubule assembly did not affect the kinetics of MAP2 phosphorylation.
Conclusions:
- Modulated phosphorylation of MAP2 significantly impacts microtubule dynamics.
- MAP2 phosphorylation acts as a regulatory switch, promoting microtubule depolymerization.
- These findings suggest a mechanism by which MAP2 phosphorylation regulates microtubule length in living cells.