Microtubule Function Flashcards
Motor proteins require __
ATP
Axonal Transport
Squid Axons (model system)
- radioactive aa injected
- proteins move along MT
- SDS-PAGE
labelled proteins travel at different speeds in cell
Kinesin
MT (+) end directed motor protein
- 2 heavy chains = head, neck, stalk (ATPase and MT binding)
- 2 light chains = recognize cargo
Functions of Kinesin
Organelle Transport
- Kinesin-1 = 2 heavy + 2 light
- Kinesin-2 = 2 heavy (heterotrimeric)
Sliding
- Kinesin-5 = 4 heavy (bipolar)
Disassembly
- Kinesin-13 = 2 heavy – head+neck
Cargo Movement
- cargo need appropriate receptor that is recognized by specific light chain
Movement of Kinesin
- anterograde
- kinesin btwn αβ dimer
- ATP hydrolysis –> kinesin has conformational change (head moves 16nm)
- linker swing forward + dock head = power stroke
Cytoplasmic Dynein
MT (-) end directed motor protein
- heavy chains = ATPase activity + stalk
- linker interact with dynactin complex – bind cargo
- ATP hydrolysis = drive movement
Dynactin Complex
- links dynein to cargo
- regulated by dynamitin (release cargo)
- p150glued binds MTs
Post-translational Modification of Tubulin
- acetylation of a lysine residue of α tubulin
- stabilize MT
Cilia vs Flagella
Cilia = 2-10μm Flagella = 10-2000μm
Axoneme
- 9+2 array of microtubules
- outer doublets — A and B tubules held with nexin
- axonemal dynein (stem - A tubule) (head reach to B tubule)
Axoneme and Basal Body
- 9 basal body triplet MTs
- A and B tubule pass transition zone. C tubule does not
Axoneme Bending
- sliding MT against each other
- NO nexin = dynein moves to (-) end + MTs slide
- Nexin = bending + no sliding
Intraflagellar Transport
- moves material “up and down”
- uses cytoplasmic dynein
Interphase Cells
Contain a non-motile primary cilium
- axonemal structure
- no axonemal dynein
Karyokinesis vs Cytokinesis
- karyokinesis = divide chromosomes
- cytokinesis = divide cytoplasm
MT Phases of Cell Cycle
Interphase = centrosome duplication
Prophase = mitotic aster separation
Metaphase = chromosomes aligned at metaphase plate
Anaphase A = chromosome move to poles
Anaphase B = spindle pole separation
Telophase = contractile ring
Cytokinesis = interphase MT array + cleavage furrow
Microtubule Stability Cell Cycle
Interphase – stable
Mitosis – unstable
- XMAP215 inhibited by phosphorylation
- kinesin-13 depolymerizes
Interphase – stable
- XMAP215 enchanes polymerize at (+) end
Components of Mitotic Apparatus
Polar MTs – microtubules grow to other pole
Kinetochore MTs – microtubules attach to chromosomes
Astral MTs – microtubules grow away from pole
Centrosome –> Mitotic Apparatus
Centromere
- attachment site for MT
- kinetochore proteins capture daughter chromosomes from each side
Spindle Formation
Polymerize + Depolymerize bring chromosome to center
- kinesin = (+) end motor protein PUSH away from pole
- dynein = (-) end motor protein PULL toward pole
- kinesin-13 = depolymerization
Capturing Chromosomes
- Ndc80 holds MT (tension = bi-orientation)
No Tension – only 1 MT attach
- Aurora B phosphorylates Ndc80 proteins
- Ndc80 lets go
Tension
- Aurora B does not phosphorylate Ndc80 proteins
- Ndc80 proteins bound to MT
Cortical Anchor Activity
- inactive = no movement
- active = dynamin and dynactin pull spindle in the direction
Anaphase A
- kinetochore MT shortening (chromosome –> pole)
- depolymerization by kinesin-13
Anaphase B
- motors (pole separation)
- Polar MTs slide by kinesin-5
- Astral MTs pulled by anchored dynein
Locate Cytokinesis Origin
- Polar MTs localize RhoGTP
- formation of contractile ring at old metaphase plate
