cours 6 - Cytoskeleton Mol Motors 2019 Flashcards
What are the general characteristics of motor protein?
- Use energy derived from hydrolysis of ATP to produce mechanical force.
- Binds to cytoskeleton (e.g. AFs or MTs).
- Produces net movement of protein or “cargo”.
- Divided into 3 families:
- Myosins: move along AFs
- Kinesins: move along MTs (toward + end)
- Dyneins: move along MTs (toward - end)
Describe myosine in general?
Very concerved head region (in all eukaryote): catalitic core that mediates hydrolysis of ATP and directs where the work is done (dark green)
What is responsable for cytokinesis?
After miosis is cytokinesis : actine filament are responsable for that
Describe myosine 2
Called the conventional muscle miosine, Important in muscle contractions and cytokinisis
Structure:
- Heavy chain : head and tail
-
Light chain (in blue and red):
- help articulate (amplify) conformation changes.
- Add flexibility to the structure
- 2 types: essential and regulatory
- Tails mediate dimerization with other myosins.(tail to tail dimer)
- Heads are catalytic, provide force.
Describe the Myosin Cycle
- Attached
- no ATP, locked phase
- 1 myosine head interacts with the actine filament.
- There is 2 head on myosine but just 1 is necessary for the transport.
- In reality, this happens simultaniously a bunch of times.
- ATP binds to the catalytic head of myosine, causing conformational change away from the actine filament (ATP causes release)
- hydrolisis of ATP occures because of catalitic activity in the myosine head. That causes the detachement but not the release of a phosphate from ATP (ADP + P). That induces a conformational change toward the + end
- weak binding to the 2nd subunitofAF, Pi release, power stroke (pulls it back), ADP lost.
- Myosine pulls the + end of the filament towards itself.
- The whole process just move red subunit
What happens when someone dies?
Rigor mortis occures because there’s no more ATP so tthe myosine bound to actine filaments cannot release it.
describe the Thick actine filament formation
- the - end of AF comes together when a muscle shortens so that the + ends are oriented in oposite directions..
- Formation of bundles in sarcomere of muscle cells.
- as the myosine molecules do their cycle, they bring the AF closer together shortening the whole structure.
- bare zone: tail tail interaction
What type of image is this?
sacromere taken with light micrograph
Describe the composition of the sacromere
Tropomyosine stabilises, move out the way to allow binding of myosine
Cap z and tropomoduline: caping protein (so they dont grow)
Z disc = α actinin (bundeling prtoein, stick inside actine filament to seperate them) + CapZ
What happens during cytokinesis?
- Redistribution of actine filaments from the perifery of the cell
- gather along the equattor froming a nettwork of actine, linked by myosine (cross-linked via their tails).
- Eventually the ring gets so small that the cytoplasm divide in 2
Describe the effect of calcium on muscle contraction
- No Ca2+, tropomyosin blocks myosin–AF binding because he is too close to actine
- Ca2+ released from Sarcoplasmic Reticulum (specialised for muscle cell) and binds to troponin C (in orange)
- Conformational change in troponin I (in beige)
- Tropomyosin (bound to Troponin T) moves and exposes binding sites
- Myosin-AF binding
- Muscle contraction
calcium is necessary for regulation. since it’s controled by nerve, the interaction in bw moter nerve to a muscle cell lead to the release of calcium. thats the way motor neurons can control muscle contraction by signalisation
describe myosine 5
- Unconventional myosin
- Regulatory subunit of the neck region are longer in myosin 5. that allows for a greater movement. (steps about 30-40nm
- Not involved in muscle contraction but in transport of cargo within the cell (that’s why they have longer neck regions: longer steps….like mike :D)
- Walks like a human: called Processivity: Always 1 head attached (not like myosin 2)
- Carries cargo (organelles).
- primarly involved in movement of cargo in the cortex (perifery of cell)
describe kinesin
- involved in transport allong MT along the lenght of the cell perticularly in neurons (axonal transport)
- moves 410 mm/day from brain to extremity
- head region concerved / tail region diverse
- c-term attached to cargo
- N-term travel on MT toward +
- exept KIFC2, that goes toward - end bc head is at c term
How was kinesins discovered?
- Studying siatic nerves of cats, kinisins where transporting the radioactive leucines away from the sites of injections.
- then MTs adhered to glass coverslips.
- Axoplasmic extract from squid giant axon + ATP induced organelle movement.
- ATP but no axoplasm, no movement.
- With non-hydrolyzable form of ATP (AMP-PNP), vesicles bound to MTs but no movement.
- Kinesin isolated and identified as motor protein.
Describe the major differences between kinesin and myosin
MT binding site for kinesin differs from the actine binding site of myosine
The non helical structure (linker) is made so that it can interact with the catalytic core in kinesin. This lead to a greater conformational change because the linker swings aroung and interact with the catalytic head of kinesin. This happens with myosine 5 but not myosin 2
Describe the kinesin cycle
•Processive steps along MTs.
- .ATP binding of leading head induces conformational change in its linker region;; trailing head advances.
- The moving force is stronger then the weak force.
- ADP induces weak binding of leading head to MT.
- Hydrolysis of trailing head induces detachment;; ADP dissociates from leading head.
- (Repeat…)
describe dynein
- (-) end directed.
- MT motor proteins.
- 2 major divisions:
- Cytoplasmic, e.g. retrograde vesicular transport.
- Axonemal, e.g. beating of cilia and flagella.
Describe Cytoplasmic Dynein
- operate in the cytosol
- Mediate the retrograde transport of vesicules/organelles (mouvement backwards towards the nucleus)
- does not attach directly to the vesicule. dynein forms a complexe with actin and that facilitates it’s bbinding to the cargo (dynactin complex
give a general description of the mouvement of myosine 5 vs kinesin
