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320Fall09Lecture19 - BIO 320 Cell Biology Fall 09 Dr Thomas...

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BIO 320 Cell Biology, Fall ‘09 Dr. Thomas Bushart Lecture 19
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Topics Filament binding proteins Filament organization Motor proteins - myosin
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Microtubule motors Kinesin and kinesin-related proteins (KRPs) Most walk towards plus end Variabilty in tails, dimerization Roles in organelle movement, microtubule stability, mitotic spindle formation and chromosome separation Dyneins Move towards minus end Variable family as well, 2 or 3 heavy chains Vesicle trafficking, Golgi localization, cilliary and flagellar movement Notably faster than KRPs
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KRPs Kinesin-5 is a bipolar tetramer, similar to myosin II thick filaments Kinesin-13* has lost motor activity Catastrophe factors Kinesin-14 moves towards minus end
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Mechanics of movement In order to move the protein must: Be able to reversibly bind to a filament Undergo conformational change Directional, expose to new binding site Nucleotide interactions drive movement and binding Unbound ATP-bound ATP hydrolysis (ADP + P i still bound) ADP-bound with P i release ADP release (return to unbound state)
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Kinesin cycle Instead of lever arm, kinesin has a linker region Motor head docks and undocks with linker region Docking moves second head forward on filament Orientation of head domains controls direction Movie
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Kinesin directionality
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Dynein
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Kinesin vs myosin ATP rigor state is different Kinesin-ATP Unbound myosin Processivity Kinesin can travel long distances DNA polymerases are another example of processive enzymes Myosin II only takes 1 or 2 steps before falling off Speed Kinesins are slower than myosins
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Processivity
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Speed Variability within a single class ATP hydrolysis rate Less time bound to track Short binding time = faster Step size
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