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
