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Reduction in microtubule dynamics in vitro by brain microtubule-associated proteins and by a microtubule-associated
P S Yamauchi1, G C Flynn, R L Marsh
1Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville.
Abstract:
Microtubule-associated protein (MAP) binding to assembled microtubules (MTs) can be reduced by the addition of polyglutamate without significant MT depolymerization or interference with MT elongation reactions. Ensuing polymer length redistribution in MAP-depleted MTs occurs on a time scale characteristic of that observed with MAP-free MTs. The redistribution phase occurs even in the absence of mechanical shearing and without appreciable effects from end-to-end annealing, as indicated by the time course of incremental changes in polymer length and MT number concentration. We also observed higher rates of MT length redistribution when the [MAP]/[tubulin] ratio was decreased. Together, these results demonstrate that MT length redistribution rates are greatly influenced by MAP content, and the data are compatible with the dynamic instability model. We also found that a peptide analogue corresponding to the second repeated sequence in the MT-binding region of MAP-2 can also markedly retard MT length redistribution kinetics, a finding that accords with the ability of this peptide to promote tubulin polymerization in the absence of MAPs and to displace MAP-2 from MTs. These results provide further evidence that MAPs can modulate MT assembly/disassembly dynamics and that peptide analogues can mimic the action of intact MAPs without the need for three contiguous repeated sequences in the MT-binding region.
Insights
Microtubule-associated proteins (MAPs) influence microtubule (MT) dynamics. Lowering MAP levels accelerates MT length redistribution, supporting the dynamic instability model.
Area of Science:
- Cell Biology
- Biochemistry
- Structural Biology
Background:
- Microtubules (MTs) are dynamic polymers crucial for cellular structure and transport.
- Microtubule-associated proteins (MAPs) regulate MT assembly, disassembly, and stability.
- Understanding MAPs' role in MT dynamics is key to deciphering cellular processes.
Purpose of the Study:
- To investigate how polyglutamate and MAP content affect microtubule length redistribution.
- To explore the mechanism by which MAPs modulate MT dynamics.
- To assess the role of specific MAP-2 peptide analogues in regulating MT assembly.
Main Methods:
- Studied the effect of polyglutamate on MAP binding to assembled microtubules (MTs).
- Analyzed MT length redistribution kinetics under varying MAP concentrations and in the presence of MAP-2 peptide analogues.
- Monitored changes in polymer length and MT number concentration over time.
Main Results:
- Polyglutamate addition reduced MAP binding without disrupting MT polymerization or elongation.
- MT length redistribution rates increased significantly with decreased MAP-to-tubulin ratios.
- A MAP-2 peptide analogue inhibited MT length redistribution and promoted tubulin polymerization.
Conclusions:
- MAP content critically influences MT length redistribution rates, supporting the dynamic instability model.
- Specific peptide sequences within MAPs can mimic the regulatory functions of intact MAPs on MT dynamics.
- MAPs modulate MT assembly/disassembly, and their functional domains can be mimicked by smaller peptide analogues.