Lecture 18: Molecular Motors and the use of the Cytoskeleton Flashcards
________ are used to convert the chemical energy of ATP hydrolysis to mechanical motion.
Molecular motor proteins
They undergo a ____ cycle of filament binding, conformational change, and filament release.
mechanochemical
____ are used for diverse processes from muscle contraction to vesicle movement.
molecular motors
Actin based motors
Myosin
Microtubule based motors
Kinesins and Dyneins
Kinesin and kinesin-like proteins
Plus-end directed motors
Dyneins
Minus-end directed motors
The first motor characterized in detail?
Myosin II
Myosin II structure
- one of the most abundant proteins in the body
- other proteins associate at neck region
- long tail is composed of coiled-coiled secondary structure
Myosin II forms ____
bipolar thick filaments
Sarcomere
- dark band = myosin II thick filaments
- light band = actin (thin filaments)
Sarcomere structure
CAP2
- actin binding protein, binds to (+) end of actin filament
- in Z disc of sarcomere
tropomodulin
- binds to the (-) end of actin filament
titin
- anchors bipolar thick filaments into Z disc
The ___ region of Myosin II is suscepltible to protease cleavage
neck region
Myosin II subdomains
How does myosin II S1 fragment work?
- myosin light chains wrap around the alphahelical segment to change position for substrate binding
The two myosin light chains are similiar in structure to ____
calmodulin
The myosin superfamily are…
plus-end directed actin motors
Which myosin has minus end movement?
myosin VI
The myosin superfamily share a ____
motor domain
Kinesin and Kinesin-related proteins are…
plus-end directed microtubule motors
Kinesin-1
- best characterized of the kinesins
- globular motor domains
Kinesin-5
- forms dimers (polar structures)
Kinesin-13
- is a catastrophin (has no motor activity
- frays the (+) end of microtubule
Kinesin-14
- minus end movement
Dyneins
- minus end directed microtubule motors
- fastest of the motors
What are the two types of Dyneins?
- ciliary
- cytoplasmic
Dynein structure
Acto-myosin Crossbridge Cycle
The myosin II ___ is the one responsible for repositioning
lever arm
Kinesin mechanochemical cycle
-Kinesin moves hand over hand
Kinesin vs. Myosin
- Kinesin binds tightly to microtubules with bound ATP
- Myosin binds tightly to actin without nucleotide (rigor state).
- The different in the time of attachment to actin allows many myosins to work in conjunction with each other.
Dynein couples ATP hydrolysis to movement in a different way
Dyneins bind to ____ which binds to ___ on vesicles
Myosin V which binds Arp1 on vesicles
Myosin V carries cargo along ___
actin filaments
Myosin V transports ___ to dendritic spines
ER
Golgi perinuclear localization depends on ____
microtubules
Name three actin based structures used for movement
- filopodia
- lamellipodia
- psuedopodia
filopodia
– Essential one-dimensional finger-like projection
– Similar to microvilli, but more dynamic
– Core of long, bundled actin filaments
lamellipodia
-Two-dimensional sheet-like structure
– Orthogonally cross-linked mesh of actin filaments
– Most is known about these due to ease of study by microcopy
psuedopodia
– Short three- dimensional projections
– Used by neutrophils and macrophages for phagocytosis
– Actin filament gel
Small G-proteins that respond to various extracellular signals to alter the actin cytoskeleton?
Rho, Rac and Cdc42
What are the results of downstream signaling of Rac-GTP?
- branched actin web in lamellipodia
- less stress fiber formation
What are the results of downstream Rho-GTP signalling?
- more stress fibers
- integrin clustering and focal adhesion formation
____ caps the plus end of actin filaments (and prevents further elongation)
the drug cytochalasin B
