Tubulin & Microtubules Flashcards

BIOS5030: Tubulin & Microtubules

Academic Year: 2023-2024Professor: Campbell Gourlay

Page 3: Microtubule Dynamics

• Microtubule Dynamics

  • Highlighted by GFP-EB1 binding to GTP-bound cap of growing microtubules.

Page 5: Microtubule-Dependent Transport

• Transport and Movements in Cells

  • Cortical capture and transport of vesicles.

  • Intraflagellar transport and exocytosis.

  • mRNA transport and pinocytosis.

  • ER morphogenesis and dynamic crosslinking of actin & microtubules.

  • Nuclear migration and endocytosis.

  • Mitochondrial transport and lysosomal transport.

  • Golgi morphogenesis and positioning.

Page 6: Tubulin Structure

• Tubulin Composition

  • Comprised of alpha (α) and beta (β) tubulin heterodimers.

  • Microtubule subunits are 10 nm protofilaments with a 50 nm lumen.

  • Important to note: GTP is involved, not ATP.

Page 7: Tubulin Binding and Hydrolysis

• Nucleotide Binding

  • Tubulin binds and hydrolyzes GTP, regulating assembly.

  • Soluble subunits exist in T form (GTP-bound) and D form (GDP-bound).

  • Polymerization follows GTP hydrolysis, with slow minus-end addition and fast plus-end addition.

Page 8: Microtubule Assembly

• Microtubule Organization

  • Nucleated at microtubule organizing centers (MTOCs).

  • Examples include centrosomes, dendrites, axons, and spindle poles.

Page 9: Centrosome Structure

• Components of Centrosomes

  • Consists of centrioles, pericentriolar material, and gamma tubulin ring complexes.

Page 11: GTP Hydrolysis and Microtubule Growth

• Growth Control

  • GTP hydrolysis controls microtubule growth.

  • GDP tubulin can peel away from the microtubule wall, leading to depolymerization.

Page 12: Dynamic Instability

• Dynamic Instability Mechanism

  • Presence of GTP-tubulin cap leads to assembly; absence leads to catastrophe and disassembly.

Page 17: Microtubule Dynamics in Cells

• In Vivo vs. In Vitro Dynamics

  • Microtubule dynamics are faster in cells (10-15 µm/min) compared to in vitro.

  • More frequent episodes of catastrophe and recovery due to microtubule-associated proteins (MAPs).

Page 18: Mitotic Spindle Formation

• Role of Centrosomes in Mitosis

  • Centrosomes duplicate and move to opposite sides of the nucleus to form the mitotic spindle.

Page 19: Regulation by MAPs

• Microtubule Associated Proteins (MAPs)

  • Regulate microtubule assembly and stability.

  • Examples include stathmin, +TIPs, XMAP215, kinesin-13, and katanin.

Page 21: MAPs in Stabilization and Destabilization

• Stabilization Factors

  • XMAP215 stabilizes growing microtubules and increases growth rate.

  • Kinesin-13 promotes depolymerization by prying apart microtubule ends.

Page 22: MAP2 and Tau Proteins

• MAP2 and Tau Functions

  • MAP2 binds along microtubule lattice; tau has a shorter cross-linking domain.

  • Differential distribution in neurons: tau in axons, MAP2 in cell bodies and dendrites.

Page 23: Stathmins

• Function of Stathmins

  • Sequester tubulin dimers, reducing the pool of free tubulin and preventing microtubule shrinkage.

  • Implicated in emotional responses and memory processing.

Page 24: Katanins

• Katanin Functionality

  • Composed of two subunits; severs microtubules and directs to centrosome.

  • Facilitates rapid microtubule shrinking during mitosis.

Page 25: Summary

• Key Points

  • Microtubules are composed of tubulin dimers that bind and hydrolyze GTP.

  • Exhibit dynamic instability regulated by various proteins.

  • These properties are crucial for biological functions of microtubules.

Further Reading

• Lodish et al. Molecular Cell Biology 7th edn. Ch. 18

• Alberts et al. Molecular Biology of the Cell 6th edn. Ch