lec 9- microtubules 2 Flashcards
(42 cards)
what are microtubule-associated proteins?
-proteins that bind to all areas of a microtubule, + end, - end, sides
-can have a variety of functions
what are the 6 types of functions microtubule-associated proteins can have?
-microtubule stabilizers (MAPs)
-microtubule nucleators (y-tubulin ring complex)
-microtubule de-stabilizers (stathmin, kinesin 13)
-microtubule severing (katanin, spastin, fidgetin)
-microtubule linking to other components (gephyrin)
-microtubule motors (kinesin, dynein)
what microtubule stabilizing proteins bind to the length, - ends, and + ends?
-length: Tau family members
- ends: y-tubulin ring complex
+ ends: EB1-EB3
how does Tau bind? what are the differences between regular and Tau labelled microtubules?
-Tau labels along the length (sides) of microtubules and stabilizes them
-in comparison to pure tubulin microtubules, Tau labelled microtubules grow 3x faster, shorten slower, and have a catastrophe only 2% of the time
how many isoforms of the single Tau gene?
7
do Tau KO mice survive?
yes, probably compensated from other MAPs
how is Tau involved with Alzheimer’s ?
-abnormal Tau de-attaches from microtubules in neurons and the de-attached Tau’s ends up tangled together, creating Tau tangles
-these Tau tangles are harmful and ultimately cause the neuron to die, which is a key factor in alzheimers
what is the y-tubuin ring complex?
-a microtubule stabilizing protein complex that includes y-tubulin and 8 other proteins
-it stabilizes and nucleates microtubules
located at the - end of microtubules
is spontaneous nucleation of microtubules favourable I living cells?
no, it doesn’t happen because its unfavourable, it is so unfavourable that a nucleator is required to nucleate
where is the y-tubulin ring complex found in round cells?
-it is found where the centrioles are at the microtubule organizing center (MTOC)
where is the y-tubulin ring complex found in polar cells?
at the top of the cell, meaning the - end is towards the membrane, the opposite of round cells
do purified y-tubulin ring complexes nucleate microtubules?
yes, but the efficiency of nucleation is very low
do microtubules still form in KO flies and worms when the spindle assembly was altered?
yes
how many types of EB microtubule stabilizing proteins are there? where do they bind on microtubules?
-3 types (EB1, EB2, and EB3)
-bind to the + ends
how is EB protein regulated?
-through phosphorylation at Ser, Thy, and Tyr residues
-this causes a change in the electrostatic interactions at the microtubule surface, which is negatively charged
what do hundreds of EB bind to on the + ends of microtubules?
bind to GTP-tubulin, function to guide microtubule growth
what does EB1 also regulate?
tubulin sheet closure
do + end-binding proteins always bind to the microtubule ends?
no
what does EB1 in yeast bind to on the microtubule? why?
it binds to the microtubule seam to help it becomes strengthened as the seam is the weakest part of the microtubule
do - ends of microtubules grow in vivo?
in vitro they do, but in vivo they don’t due to multiple capping proteins that stabilize that side
what is CAMSAP (calmodulin-regulated spectrin-associated proteins) ?
a microtubule - end-binding protein
how many members of CAMSAP? what were the code names?
3 types: CAMSAP 1, CAMSAP 2(KIAA1078/CAMSAP1L1) and CAMSAP 3 (KIAA1543/Nezah)
was Nezah first shown to bind to microtubule - ends?
yes
what was patronin first shown to do in Drosophila?
bind to - ends of microtubules to protect them from destabilizing motor proteins like kinesin 13
