Lecture 16 Flashcards
What type of protein is Augment?
MAP (microtubule Associated Protein)
How does Augmin bind to microtubules?
Alpha/beta subunits have tails that are rich in aspartic/glutamic acid whcih means they are negatively charge. Augmin is a positively charged protein that can bind through electrostatic interactions to these tails
What does Augmin do?
Acts as a nucleating center by recruiting ring complexes
Tubulin sequestering protein?
Stathmin
What does stathmin do?
Binds to two tubulin dimers and prevents their addition to a microtubule
-Decreases the concentration of free tubulin subunits , increases probability that a microtubule will shrink
What side of the tubulin does the stathmin cover?
-The alpha side prevents binding to positive
How does phosphorylation affect stathmin?
Reduces stathmins ability for tubulin which increases microtubule growth
Microtubule End binding proteins?
-Kinesin-13
-XMAP215
Kinesin-13?
-Binds near the plus end of microtubules and induces catastrophe
How does Kinesin-13 cause catastrophe?
-binds ATP near the plus end of the microtubule which increases monomer growth but kinesin binds the monomers and forms them into a curve shape which leads to catastrophe
Where does XMAP52 bind?
Near the plus end of microtubules
What does XMAP52 do?
-promotes microtubule growth by binding to the plus end of the microtubule with its N-terminus and its C-terminus has a large affinity for free tubulin
Katanin?
-Microtubule severing protein
-AAA ATPase
-Small subunit ATPase
-Large subunit binds microtubule
How does Katanin work?
-ATPase domain hydrolyzes ATP and uses the energy to grab onto the negative tails of the alpha/beta subunits and pull on them. They do this till they pull the subunit out of the microtubule creating a hole.
How does Katanin promote microtubule growth?
-The hole created by katanin gets filled in by free GTP bound tubulinsK
Katanin can stop catastrophe?
-newly added GTP bound tubulins can prevent the microtubule from breaking down
Structure of Kinesin ?
-N-terminal motor domain that can bind the microtubule and hydrolyze ATP
-Flexible neck region that can bend back and forth during hydrolysis
-tail region made up of alpha-helices that can form coiled-coil
Which direction do kinesins move?
-Most have their motor domain in the N-terminus and move toward the positive end
-Some kinesins have their motor domains in the C-terminus and move toward the minus end
Kinesin ADP bound?
-Loose association with microtubule
ADP release and binding of new ATP?
-Kinesin tightly associates to microtubule
-Neck faces toward plus end
ATP hydrolysis?
-Neck shifts back to minus end
-Microtubule association weakens
Do kinesins function in a coordinated fashion?
Yes
Kinesins coordinated movement?
- Lagging head bound to ATP (tightly associated) and leading head bound to ADP(loosely associated)
- Lagging head hydrolyzes and leading head releases ADP and binds ATP. Lagging head neck flips over leading head toward the plus end.
- Now lagging head is infront and becomes the new leading head
T/F: One kinesin head is always bound to ADP and one is always bound to ATP?
True
How do kinesins bind cargo ?
Through their C-terminal tails
-Can bind cargo directly to the tail or indirectly via an adaptor protein
Which direction do dyneins walk?
Toward the minus end of the microtubule
What is the largest motor protein?
Dynein
Structure of dynein?
-Catalytic head(ATPase)
-6AAA subunits but only one is functional
-Stalk region binds microtubule
-Tail domain binds cargo
Axonemal Dyneins?
-found in cilia and are responsible for the beating of cilia
Kinesins and Dynein in cells?
-Microtubules shoot out from the MTOC
-Kinesins walk to ward the plus end to the peripheries of the cell
-Dynein walks toward the minus end toward the center of the cell
Where are intermediate filaments important?
Hair/Skin
What are intermediate filaments made of?
-Alpha-helical filaments tat wind together to form coiled-coil dimers
-These dimers line up antiparallel to make tetramers
-8 tetramers form an intermediate filament
Can intermediate filaments transport cargo?
No, since they have no polarity
Examples of intermediate filaments?
-Nuclear lamins(prevent squeezing of cell)
-keratins
-Neurofilaments
-Desmins
