9 – Microtubule Motors Flashcards
…Drives long-range transport
Motor proteins
Movement of organelles
- to +
+ to -
- to + = secretion
+ to - = cargo from plasma membrane inward
Secretory vesicles – carried by…
carried to…
carried by Kinesins
Toward periphery of cell
Transport can be…
example
activated/inhibited by signaling molecules
melanosomes in frog for color changing
melanosomes & concentration of cAMP
Changing concentration of cAMP
Low cAMP = aggregates melanosome
-Darker color on frog
High cAMP = dispersed melanosome
-Lighter color on frog
Microtubules are …
Roadway for transport of organelles
Design problems for transport (4)
-How to put one foot in front of the other?
-Some cargo in, some out?
Have to be bidirectional
-How to select cargo? - Must grab the right things
-Which road to take? - The right direction/microtubule
motor protein – walks to the microtubule + end
Kinesin
-converts chemical energy into mechanical work
kinesin structure
Motor domain = head
-linker domains connect to coiled coil stock made of alpha helices
Cargo binding = tail & light chain
Kinesin transport…
vesicular cargo
kinesins is worlds…
Worlds tiniest biped
kinesin can only walk for…
Can only walk for 1-2 seconds before it falls off ~100 steps
how does Kinesin WALK
1.Kinesin encounter microtubule with ADP in both heads
2.Microtubule binding releases ADP from forward/leading head
-locks motor domain onto microtubule
3. Binding of new ATP into forward head – induces conformational change
4.Neck linker swings the rear – trailing head forward
5. New forward head releases ADP, binds tightly - trailing head hydrolyzes ATP& release Pi
how do kinesin know when to hydrolyze ATP & release Pi
mechanical stress & strain
STRAIN:inhibit ATP binding to front & accelerate hydrolysis in the back
STRAIN released = when phosphate is released
new ATP combined necklinker swing - low rate ATP hydrolysis - STRAIN
-when both heads facing down, rear head experience force vector up & pulled forward - accelerate ATP hydrolysis
minus end directed motor protein
Dynein - has 6 ATPases
ATPase domain of dynein
rotates to move motor
Dynein motors power
beating flagella
Tug of war between opposing dynein = give rise to flagellar beat
How to select cargo?
Motor protein cargo - Selected by adapter proteins
-Dynein responsible for all inward transport
Different cargo
= different adapter (dynein)
…connected by dynein
Doublet microtubules of axonemes
outbound transport is managed by
kinesis
inbound transport is managed by
1 motor, but has a wide range of cargo adapters to pick which cargo to move things inward
Which road to take?
Post-translational modification of tubulin = marks different microtubule roads
Tubulin code – different regions = different modification
