The Core ATPase Domains of Cytoskeletal Motors Flashcards
What is the structure of P-loop NTPases?
- An alpha and beta strand
- The beta strand forms a central mostly parallel sheet, surrounded on both sides by alpha helices
What family are dyenins part of?
AAA+ family
What family are myosin and kinesins part of?
What mechanical elements provide the powerstroke in myosin?
Converter domain and lever arm
What mechanical elements provide the powerstroke in kinesin?
the neck linker
What is a powerstroke?
A large, rapid structural change in protein conformation used to do mechanical work
What size is a powerstroke?
On the order of a protein (nm)
What drives a power stroke?
- Changes in the nucleotide bound state switches the protein from structural state 1 to 2
What are thre features of the power stroke of myosin?
- The lever arm moves from a pre-stroke position forward towards the + end
What does myosin move along?
Actin
What does the step size of myosin power strokes depend on?
Lever arm length
What are the features of the kinesin power stroke?
- Neck linker docks against the motor core
- The powerstroke moves the C terminus of the necklinker
What is the track for kinesin?
Microtubule protofilaments
How large is each kinesin step?
8nm
Why is each kinesin step 8nm?
It is the distance between binding sites on microtubule protofilaments
Which direction do most kinesins move?
From + end to - end
What constrains the step size for kinesin?
The power stroke
Does the power stroke always occur at ATP hydrolysis?
No, storage and release of free energy can occur at any stage in the cycle
In order to change conformational changes between ATP and ADP bound states what must motor proteins sense?
The prescence or abscence of a single phosphate group
What is the sensor in motor proteins comprised of?
- 2 loops which are switch 1 and 2
How does the sensor work in motor proteins?
- ATP binding engages sensor
- sensor moves forward to contact gamma phosphate
- Phosphate release disengages the sensor
How are movements of the sensor relayed to other parts of motor proteins?
- Via alpha-helix relay
- kinked conformation occurs when ATP bound
- movement if relay helix changes the conformation of the converter domain
What is duty ratio?
The time spent in free or bound states during ATPase cycle
In kinesin what binds to tubulin?
12 amino acid loop
In myosin what binds to actin?
140 amino acid domain
What is coupling efficiency?
The number of ATPs used to make 1 step
How can the rate of motor proteins be measured?
- linear distance moved per unit time
- Or
- ATPs hydrolysed per unit time
