Molecular Motors II Flashcards
Explain the Cytoplasmic Dynein ?
- Trafficking of multiple cargo (Membraneous compartments, mRNA, specific proteins, viruses, aggregated proteins and nuclei
- Moves towards minus ends of microtubules
- Binds to α-β tubulin dimer
- Large multi-subunit protein complex composed of two identical heavy chains and multiple light chains
- N-terminal tails
- dimerisation/LC binding/cargo binding - Linker
- lever arm - C-terminal AAA+ ring and coiled coil stalk
- Motor and microtubule binding
Explain the distinct motor of cytoplasmic dynein ?
- Motor different to kinesin/myosin
- Six repeated AAA+ domains
- Folds to form a linked hexamer
- Coiled-coil domain with microtubule-binding domain (MTBD) pokes out from AAA+ ring
Linker domain runs across face of AAA+ hexamer - Tail dimerises two dyneins (flagella forms are monomeric)
Explain the binding in a Cytoplasmic Dyenin ?
- ATP binding by AAA+ ring causes conformation change
- Relative position of linker and coiled-coiled change
- Communication to MTBD (microtubule binding domain)
- Binding of ATP weakens binding to microtubule
- Number of ATPs required unclear
Cytoplasmic Dynein –motors move in 16 nm steps. It’s active as ?
- Active as a dimer
- Processive Motor with high duty ratio
- Labelling of one motor of a dimer reveals hand-over-hand mechanism
- However, step size more variable and back steps frequent
On average, centre of dimer moves in 8 nm steps whilst motor moves ?
In 16nm steps
What is the Axial path for kinesin ?
Axial path for kinesin is straight –sticks to one protofilament
What is the Axial path for dynein ?
Axial path for dynein is more variable – can step between protofilaments
Explain the Flagella ?
- Used for propulsion of both bacterial and eukaryotic cells. Rotate.
- Flagellate bacteria . Eg. Salmonella
- Flagellate eukaryotic cell. Eg. Sperm cell
- Cilia –similar to flagella in composition (generally shorter). Beat back and forth
Microtubules in Cilia & Flagella in Eukaryotes ?
- MTs are the fundamental structural unit in cilia and flagella
- Form the Axoneme
The dynein “cargo”in cilia movement is ?
The A-tubule, moves along the B-tubule
Molecule motors in intracellular transport –Core similarities ?
- Motion requires the hydrolysis of ATP
- Motors evolved to move on either actin or microtubules
- Directional
- Action of two motors
- Hand-over-hand motion
- Processive
What class is muscle myosin?
Muscle myosin is of the myosin II class
Explain Myosin V in depth ?
- Membrane trafficking
- Moves towards plus ends of actin
- Most studied myosin
- Dimer of two heavy chains (200kDa) and multiple light chains
- N-terminal globular myosin motor domain ATPase/motor
- Six IQ motifs with binding sites for light chains - three times longer than in myosin II
- Rigid lever arm/regulation
- Coiled coil domain
- C-terminal globular cargo binding domain and further light chains
- Active as a dimer (of heavy chains)
- Processive Motor with high duty ratio
What does the ATPase cycle brings about ?
Conformational change in converter domain
What does the light chain-binding region serve as in myosin ?
It serves as a lever arm to amplify movements of the converter domain, which transitions between pre-stroke and post-stroke configurations
For myosin II, short lever arm results in ?
10nm displacement of lever arm
For myosin V, longer lever arms result in ?
~37 nm displacement of lever arm
Explain Myosin VI in depth ?
- Membrane trafficking
- Moves towards minus ends of actin
- Dimer of two heavy chains and multiple light chains
- N-terminal globular myosin motor domain plus special insert domain
- ATPase/motor - Two IQ motifs with binding sites for light chains
- Rigid lever arm/regulation - Proximal tail
- lever arm extension - Medial tail coiled-coil
- C-terminal distal tail/cargo binding domains
What does the Inserted region cause ?
Light chain redirects the myosin VI light chain-binding region in a direction opposite to that of myosin V
Explain the motion of molecular motors ?
- Motion is coupled to NTPaseactivity
- Motion is produced by conformational changes
- Motion is “actioned” by changes in affinity for binding partner eg. for Microtubules
- Changes in affinity are related to the conformational changes
- Conformational changes are driven by NTP hydrolysis and release of products.
What are some diseases associated with deficient motor proteins ?
- Charcot Marie Tooth disease type 2A (human) :
- Mutation in Kinesin KIF1Bβ which is specialised to transport mitochondria, leads to a progressive loss of muscle tissue - Motor neuron disease (Amylotrophiclateral sclerosis ALS):
- Mutations in cytoplasmic dynein in MICE leads to ALS (e.g. Legs at odd angles) - Griscelli disease (human):
- Mutations in the human myosin V gene result in ataxia, light pigmentation and a variety of immuno-deficiencies and neurological based symptoms
- Impaired transport of melanosomes
- Impaired neuronal function and immune system - Spinal muscular atrophy with lower extremity predominance (SMALED)
- 30 missense mutations in dynein identified in human patients.
