Myosin Motion Flashcards
Which direction does myosin VI move?
towards the minus end
Which direction does myosin V move?
Towards the plus end
What does the number of IQ motifs in the lever arm of myosin dictate?
How many light chains bind
What is the function of myosin V?
Membrane trafficking
What kind of duty ratio does Myosin V have?
High duty
What is the structure of myosin V?
- Active as dimer of heavy chains
- N-terminal globular myosin motor ATPase
- 6 IQ motifs with binding sites for light chains
- C-terminal globular cargo binding domain and further light chains
How many IQ motifs does myosin V contain?
6
What tracks does myosin V use?
- Cytoskeletal actin monomer proteins
- 2 strand helical bundle
How frequently do equivalent binding sites occur on cytoskeletal actin?
Every 36nm
What kind of mechanism does myosin V use?
Hand-over hand movement
How far does myosin V cargo move in one step?
36nm
For one step how far does the myosin V motor move?
72nm
What technique was used to label the myosin V cargo and motor?
FIONA
What function does the light chain serve in myosin V?
The light chain binding region serves as a lever arm to amplify movements of the converter domain
What does the converter domain transition between?
Pre and post stroke configurations
What is the angle between the pre- and post- stroke converter domain in myosin V?
70º
In myosin V the long lever arm results in displacement of lever arm by what distance?
~37nm
What is the rate limiting step for Myosin V?
ADP release
At what point in the ATPase cycle does the power stroke occur in myosin V?
Once ATP has been hydrolysed and when ADP is still bound
In myosin V when does the lever arm move to the pre-stroke position?
Directly after ATP hydrolysis
When is myosin V unbound from actin?
During ATP hydrolysis
What happens after the power stroke?
The protein enters a strained waiting state
Why does partial execution of the power stroke occur in myosin V?
it can’t complete it due to the other motor being in the ADP bound state
What couples the ATP cycles in myosin V?
The ADP bound motor being pulled by mechanical force of the powerstroke, entering the strained waiting state
What causes accerlation of ADP release in myosin V?
Mechanical strain
What are the similarities between myosin V and kinesin?
- processive dimer of 2 motors
- directional movement along track
- hand-over-hand mech requiring coordination
- 1 ATP used per step
- High duty
How many ATP are used per step in myosin V?
1
What are the differences between myosin V and kinesin?
- Myosin V much larger step size
- different tracks and binding sites
- Quite different coupling
What is the function of myosin VI?
Involved in membrane trafficking
Which direction does myosin VI move?
Towards the minus end
What mechanism does myosin VI use?
Hand-over-hand
What is the structure of myosin VI?
- dimer of 2 heavy chains and multiple light chains
- N-terminal globular myosin motor domain and special insert domain after converter
- Coiled-coil structure
What is the main structural difference between myosin V and myosin VI?
Special insert
How many IQ motifs does the lever arm of myosin VI contain?
1
What allows myosin VI to move backwards?
Special insert domain
What are the effects of the special insert in myosin VI?
- Introduces a kink in the helix
- Alters the angle between pre and post powerstroke states
What is the effect of a kink in the lever arm of myosin VI?
- Reverses orientation of lever arm, reversing pre and post stroke positions
- alters angle between pre and post stroke states
In myosin VI the kink the lever arm makes the angle between the pre and post stroke states what?
180º
In myosin VI which direction does the post stroke state point to?
The minus end
How can myosin VI contact actin binding sites 36nm apart?
3 helix bundle proximal tail can undergo an unfolding transition which allows it to stretch and extend the short lever arm
