The Core ATPase Domains of Cytoskeletal Motors

Question 1

What is the structure of P-loop NTPases?

Answer 1

• An alpha and beta strand
• The beta strand forms a central mostly parallel sheet, surrounded on both sides by alpha helices

Question 2

What family are dyenins part of?

Answer 2

AAA+ family

Question 3

What family are myosin and kinesins part of?

Question 4

What mechanical elements provide the powerstroke in myosin?

Answer 4

Converter domain and lever arm

Question 5

What mechanical elements provide the powerstroke in kinesin?

Answer 5

the neck linker

Question 6

What is a powerstroke?

Answer 6

A large, rapid structural change in protein conformation used to do mechanical work

Question 7

What size is a powerstroke?

Answer 7

On the order of a protein (nm)

Question 8

What drives a power stroke?

Answer 8

• Changes in the nucleotide bound state switches the protein from structural state 1 to 2

Question 9

What are thre features of the power stroke of myosin?

Answer 9

• The lever arm moves from a pre-stroke position forward towards the + end

Question 10

What does myosin move along?

Answer 10

Actin

Question 11

What does the step size of myosin power strokes depend on?

Answer 11

Lever arm length

Question 12

What are the features of the kinesin power stroke?

Answer 12

• Neck linker docks against the motor core
• The powerstroke moves the C terminus of the necklinker

Question 13

What is the track for kinesin?

Answer 13

Microtubule protofilaments

Question 14

How large is each kinesin step?

Answer 14

8nm

Question 15

Why is each kinesin step 8nm?

Answer 15

It is the distance between binding sites on microtubule protofilaments

Question 16

Which direction do most kinesins move?

Answer 16

From + end to - end

Question 17

What constrains the step size for kinesin?

Answer 17

The power stroke

Question 18

Does the power stroke always occur at ATP hydrolysis?

Answer 18

No, storage and release of free energy can occur at any stage in the cycle

Question 19

In order to change conformational changes between ATP and ADP bound states what must motor proteins sense?

Answer 19

The prescence or abscence of a single phosphate group

Question 20

What is the sensor in motor proteins comprised of?

Answer 20

• 2 loops which are switch 1 and 2

Question 21

How does the sensor work in motor proteins?

Answer 21

• ATP binding engages sensor
• sensor moves forward to contact gamma phosphate
• Phosphate release disengages the sensor

Question 22

How are movements of the sensor relayed to other parts of motor proteins?

Answer 22

• Via alpha-helix relay
• kinked conformation occurs when ATP bound
• movement if relay helix changes the conformation of the converter domain

Question 23

What is duty ratio?

Answer 23

The time spent in free or bound states during ATPase cycle

Question 24

In kinesin what binds to tubulin?

Answer 24

12 amino acid loop

Question 25

In myosin what binds to actin?

Answer 25

140 amino acid domain

Question 26

What is coupling efficiency?

Answer 26

The number of ATPs used to make 1 step

Question 27

How can the rate of motor proteins be measured?

Answer 27

• linear distance moved per unit time
• Or
• ATPs hydrolysed per unit time