Lecture 14 : Moving Cargo within Cells

Question 1

What are motor proteins

Answer 1

Enzyme protein that converts chemical energy to mechanical energy (ATP -> Movement)

Hydrolysis of ATP + conformational changes = movement

Actin based and microtubule based.

Question 2

What are the actin based motor proteins?

Answer 2

Myosin VI and myosin V

Question 3

What are the microtubule based proteins

Answer 3

Dyneins and Kinesins

Question 4

Structure of Myosin

Answer 4

Head domain
- Binds to F actin filament
- Binds to ATP
- The part of the enzyme where hydrolysis of ATP occurs to generate a conformational change which induces mechanical movement

Neck domain
- Links the head and tail
- Lever transducing force generated by the head
- Quite a short domain

Tail domain
- Variable
- Site where motor protein interacts with cargo

Not structure, but ALWAYS MOVES TOWARDS + END OF ACTIN (except myosin IV). Important in cytokinesis, transport etc

Question 5

What is the structure of myosin II (muscle myosin, conventional myosin)

Answer 5

• 6 polypeptide chains
• 2 large heavy chains (200 kDa each)
• 4 light chains (20 kDa each)

Question 6

Summarise the Actin-Myosin Crossbridge Cycle

Answer 6

Non-processive motor, uncoordinated attachment of myosin heads to actin

Question 7

Summarise the myosin V cycle

Answer 7

1. Myosin V has both heads attached, but the leading head has ADP bound
2. ATP binds to the trailing head, head dissociates from actin filament
3. ATP hydrolysed to ADP + Pi, induces conformational change, lunging trailing head forward to become new leading head
4. New leading head binds to actin, Pi is released
5. ADP released from new trailing head (old leading head) and cycle begins again

Question 8

How is non-muscle myosin II regulated

Answer 8

1. Exists by default in inactive FOLDED state
2. Phosphorylation by MLCK occurs on regulatory light chain
3. Myosin II becomes activated

Question 9

Structure of microtubule motors

Answer 9

Head domain
- binds to microtubule and ATP
- ATP hydrolysis generates force

Neck domain
- Links head and tail

Tail domain
- Interacts with cargo molecules

Question 10

What are the 2 types of kinesin

Answer 10

Cytosolic
- Move vesicles or organelles around microtubule tracks
- Move towards + end

Spindle
- During spindle assembly in cell division
- Move towards - end

Question 11

Kinesin mechanism of walking looks the same as myosin V, same as inhibition

Question 11

What are Dyneins

Answer 11

Microtubule motor protein, 2 classes

Cytosolic - movement of vesicles and chromosomes
Axonemal - beating of cilia and flagella