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- 3 classes: 1 cytoplasmic, 2 axonemal(outer and inner arm)
- Multiple genes per genome: 7 in Dros.
- direct towards negative end
- dimers, some trimers
- AAA ATPase superfamily
What are the three major classes of motor proteins and what type of filaments does each move along?
- 1.Myosin: Transports vesicles along ACTIN filaments, used for muscle contraction
- 2.Kinesin: Walks towards the plus end of MICROTUBULES, anterograde axonal transport
- 3.Dynein: Walks towards the negative end (retrograde) of MICROTUBULES, motor for cilia and flagella retrograde axonal transport
Do all motor proteins "walk" in the same direction along cytoskeleton filaments? If no, what is the significance of directionality for the cell? Provide some examples of motors that walk in different directions.
- The structure of these proteins dictate if they will be moving in the forwards or reverse direction.
- Myosin: most walk towards the barbed (positive) end of actin filaments (Myo 6 goes towards neg). Most of these are dimers, but some monomers
- Kinesin: most walk towards the Positive end, except for 14, which is C terminal directed, walking towards the negative end. Most dimerize except for Kinesin 3 (monomer)
- Dyneins: mostly all walk towards negative end of microtubules. All are dimers, or trimers
Compare and contrast the movement generation mechanisms of the myosin and kinesins.
- All 3 use similar principles to generate force, utilizing ATP
- Both come from NTPase superfamily
- Myosin and kinesin have similar structures, they evolved from common ancestor, calcium is involved in both of these mechanisms. They both are involved in intracellular movement, both anterograde. Myosin is, however, also involved in sliding the microfilaments in muscle contraction and cytokinesis
- Myosin mechanism involves the the first step of ATP hydrolysis, with Pi still attached. The myosin binds to actin here, and once Pi is released this is the POWER STROKE. The ADP is also released, then the binding of ATP causes the myosin to RELEASE from actin.
- Kinesin is similar to myosin 5, in which 2 motor domains act in sequence to generate a step by step movement along microtubule. In this case however, the BINDING of ATP causes the POWER STROKE. What occurs is ADP is released from one domain which is attached to MT, and when ATP comes in to replace it, it triggers the other domain to shift and attach ahead of the first. Then that first domain hydrolyzes ATP and releases the phosphate from its group, and as its neck linker is unzippering from the first head, the ADP from the second domain is released and ATP comes in to continue the cycle.
Compare and contrast the movement generation mechanisms of the kinesins and dyneins.
- Dyneins are dimers or trimers, whereas kinesins exist in dimers and can also be monomers
- Kinesins are from NTPase superfamily, and Dyneins are from AAA ATPase superfamily
- They have similar POWER STROKES, both occurring when ATP binds to the domain
- They both are involved in intracellular motility, with dynein retrograde and kinesin anterograde
- Dyneins can cause sliding of microtubules in axonemes (cytoskeletal structure of appendages of cilia and flagella)
- Dynein mechanism involves the binding of ATP, which induces the POWER STROKE, followed by the release of ADP. The ATP is then hydrolyzed and both ADP and Pi are released, followed by ATP binding, which continues the cycle.