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A microtubule-associated protein (MAP2) kinase restores microtubule motility in embryonic brain
1Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Abstract:
Motility driven by the microtubule motors, kinesin and cytoplasmic dynein, is inhibited by MAP2 (López, L. A., and Sheetz, M. P. (1993) Cell Motil. Cytoskeleton 24, 1-16). The MAP2 inhibition is reversed by a kinase that is co-purified with chicken embryonic MAP2, completely releasing MAP2 from the microtubules. We have identified this activity with a kinase, embryonic MAP2 kinase (M(r) = 100,000), which phosphorylates MAP2 at serine amino acid residues. This kinase is c-AMP independent and inhibited by potassium fluoride and glycerol 2-phosphate. Only the phosphorylation produced by embryonic MAP2 kinase can change the affinity of MAP2 by microtubules. Bovine MAP2 kinase, Cdc2 kinase, mitogenic activated protein kinase, and the NIMA kinase are able to phosphorylate MAP2 but do not change the affinity for microtubules. In vivo, embryonic MAP2 kinase could play a major role in the regulation of motility and positioning of membranous organelles within the cells even at substoichiometric levels.
Insights
A novel embryonic MAP2 kinase phosphorylates MAP2, reversing microtubule motor inhibition. This specific phosphorylation regulates MAP2-microtubule affinity, impacting cellular organelle positioning and motility.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Microtubule-based motility relies on kinesin and cytoplasmic dynein motors.
- Microtubule-associated protein 2 (MAP2) inhibits these motors.
- A co-purified kinase activity reverses MAP2-mediated inhibition.
Purpose of the Study:
- To identify and characterize the kinase responsible for reversing MAP2 inhibition.
- To determine if this kinase affects MAP2's affinity for microtubules.
- To explore the in vivo role of this kinase in cellular processes.
Main Methods:
- Co-purification of kinase activity with chicken embryonic MAP2.
- Kinase assays to assess MAP2 phosphorylation and microtubule binding.
- Testing various kinases for their ability to phosphorylate MAP2 and alter its microtubule affinity.
Main Results:
- Identified embryonic MAP2 kinase (100,000 M(r)) that phosphorylates MAP2 at serine residues.
- This phosphorylation specifically alters MAP2's affinity for microtubules.
- Other tested kinases (Bovine MAP2 kinase, Cdc2, MAPK, NIMA) phosphorylate MAP2 but do not change its microtubule affinity.
- The identified kinase is cAMP-independent and inhibited by fluoride and glycerol phosphate.
Conclusions:
- Embryonic MAP2 kinase is crucial for regulating MAP2-microtubule interactions.
- Specific phosphorylation by embryonic MAP2 kinase releases MAP2 from microtubules, thereby reversing motor inhibition.
- This kinase has potential in vivo roles in regulating organelle motility and positioning, even at low concentrations.