The cytoskeleton Flashcards
Why do eukaryotic cells need a cytoskeleton?
- large
- cannot rely on diffusion
- need motors & tracks
Quick facts about Actin filaments?
- 7nm
- polymer of actin
- tracks for myosin
Quick facts about Microtubules?
- 25nm
- polymer of alpha-beta tubulin dimers
- tracks for kinesin and dyenin
Quick facts about Intermediate filaments?
- 10nm
- polymers of intermediate filament proteins
- no associated motors
How do Microtubules help a cell develop polarity?
- minus end in centrosome
- plus end towards plasma membrane
What is the structure of Microtubules?
- alpha-beta tubulin dimers = 8nm
- b-tubulin ‘plus’
- a-tubulin ‘minus’
- 13 protofilaments
Which ends of the microtubules are fast/slow growing?
'plus' = fast 'minus' = slow
What is involved in the MTOC?
- microtubules grow out of MTOC
- centrioles
- pericentriolar matrix
What is involved in the polymerisation and depolymerisation of microtubules?
GTP-tubulin subunits add to ‘plus’
if stops - GDP capped tubulin - peeling behaviour
GTP-tubulin CAP lost = depolymerise - catastrophe
only b-tubulin hydrolyses GTP - exposed at ‘plus’
How can microtubules be post-translationally modified?
C-terminal tail = polyglutamated/glycalated
C-terminal tyrosine removed
3 roles of microtubules?
1) trafficking of cargo
2) mitosis
3) Cilium
How does the motor protein Kinesin use Microtubules as tracks?
traffics to ‘plus’
takes 8nm steps
ATP hydrolysis powered
40 diff. types
What is the structure of kinesin motor protein?
Dimer
2 motor domins
tail can bind to light chains
How are kinesins important in mitosis?
trafficking of EG5
EG5 tetramer binds between microtubules
builds spindle
How does the motor protein Dynein use microtubules as tracks?
- traffics to ‘minus’
- cytoplasmic dynein 1 & 2
What is the structure of Dynein motor protein?
- triple A ring made of 6 triple A motifs
- linker
- found in cilia & cytoplasm
What is the Dynein power stroke?
linker goes across top and hits across AAA2-4
steric clash when linker is hit
linker moves out way forming bent conformation = pre-power stroke conformation
What are MAPS?
microtubule associated proteins
Whats is TAU protein?
disease protein
mainly in axons
stabilises microtubules
small amount in DNA suggesting nuclear function
How is binding of TAU to microtubules regulated?
by phosphorylation
TAU affinity for MTs decreases when hyper-phosphorylated
What is Spastin?
disease protein
severs stable regions of microtubules
ataches to C-terminal tubulin ‘tails’ - dislodges tubulin from MT lattic
How is severing by Spastin stimulated?
polyglutamationf of C-terminal tubulin tail by TTLL6
How are microtubules involved in mitosis?
form scaffold for sorting chromosomes
form spindle
dynein & kinesins involved
How are microtubules involved in Cilia?
motile or immotile
motile have pair of central microtubules
‘9+2’ - 2 central microtubule surrounded by 9 MT doublets
How are Kinesin and Dynein-2 involved in cilia?
traffic intra-flagellar (IFT) cargoes
build/maintain all cilia
What are diseases associated with microtubules?
TUBA1A - polymcirogyria - small gyri
TUBB2B - Diffuse pachygyria - smooth brain
How do neurons migrate in the developing brain?
neural progenitors in ventricular zone migrate to cortical plate
migration in cerebral cortex & hippocampus
What do mutations in TUBA1A cause?
affect binding of kinesins
affect polymerisation
microlissencephaly
lissencephaly
pachygyriA
polymicrogyria
What happens in Lissencephaly?
- smooth brain
- small head
- mental retardation
What are 2 common mutations in TUBA1A?
- R402H
- R264C
affect binding of proteins to MTs
reduced traficking
reduced microtubule stability
What do mutations in kinesins cause?
hereditary spastic paraplegia
What happens in hereditary spastic paraplegia?
- Kif5a
- 56 missense
- in motor domain
- spasticity in legs
- kinesin movement affected
- problems at synapses
What are the mutations in Kif5a that causes SPG?
reduce velocity - N256S, K253N
reducing binding - R280S, K253N
What diseases is TAU protein involved in?
Alzheimers
Progressive supranuclear palsy
Cortico-basal degeneration
dementia
parksinsonism
What are the mutations in TAU protein?
- in microtubule binding domain
- reduced affinity for microtubules
- aggregation
missense & splicing mutatons
How does TAU cause disease
detach from microtubules
microtubule disassembly
reduced trafficking
misolocalisation to presynapse
synaptic dysfunction
What is the synaptic dysfunction of Tau?
Tau recruits enzyme TTLL6
polyglutamates tubulin
Tau unbinds
Spastin recruited
severs & destabilises
What is taxol?
microtubule stabilising drug
cancer treatment
induces mitotic arrest
cell death results from chromosome mis-segregation on multipolar spindles
What is involved in ciliopathies?
kinesin and dynein
lots of syndromes
What does mutation in dynein heavy chain cause?
PCD - primary cilia dyskinesia
altered bending of distal region
ability of dynein heavy chain to generate movement
