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Cold depolymerization of microtubules to double rings: geometric stabilization of assemblies
R Melki1, M F Carlier, D Pantaloni
1Centre National de la Recherche Scientifique, Laboratoire d'Enzymologie, Gif-sur-Yvette, France.
Biochemistry
|November 14, 1989
Summary
Microtubule depolymerization involves GDP-tubulin subunits rapidly forming curved oligomers, not direct protofilament coiling. Ring disassembly is slower than nucleotide exchange, supporting a two-conformation tubulin model.
Area of Science:
- Biochemistry
- Cell Biology
- Structural Biology
Background:
- Microtubules are dynamic polymers essential for cellular processes.
- Understanding microtubule depolymerization kinetics is crucial for cell biology.
- Previous models suggested direct protofilament coiling during disassembly.
Purpose of the Study:
- To elucidate the kinetic pathway of microtubule depolymerization at 0°C.
- To investigate the role of tubulin conformations and nucleotide binding in disassembly.
- To test existing models of microtubule assembly and disassembly.
Main Methods:
- Depolymerization of microtubules (MAP-containing and MAP-free) at 0°C.
- Use of radiolabeled GDP, GTP, and dimeric tubulin ([3H]GDP, [3H]GTP, 125I).
- Separation of depolymerization products via column chromatography and structural identification via electron microscopy.
Main Results:
- Two predominant non-microtubule states: alpha-beta dimers and double rings.
- GDP-tubulin subunits rapidly equilibrate with curved oligomers, acting as kinetic intermediates.
- Ring formation from dimers is faster than nucleotide exchange; ring disassembly is significantly slower, especially with MAPs.
Conclusions:
- Microtubule ring formation does not involve direct protofilament coiling.
- Results support a model of two tubulin conformations (straight and curved) controlled by nucleotide binding.
- This equilibrium explains spontaneous oscillations in microtubule assembly dynamics.