Molecular Motors
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Transcript of Molecular Motors
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Molecular MotorsLecture 33 ` BSCI 420/421 Nov 18, 2002
“To survive the 21st century, our thinking must be creative and humane as well as analytical.”
- Robert Kuhn
1. Myosins2. Kinesins3. Dyneins
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1. Myosins • Are a family of motor proteins that bind to & move along actin filaments toward the + ends.
• Large globular heads bind and split ATP
• Undergo a configurational change that changes the angle of the head with respect to an -helical tail. E.g. Myosin II
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Myosin II of vertebrate muscle
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The Myosin family portraitN--------------------------------C
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In vitro motility assay: Evidence of myosin’s motor activity(Fig. 53) (wrong way)
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X-ray crystal structures of myosin & kinesin heads
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Myosin cross-bridge cycle
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Skeletal Muscle fibers are multinucleate muscle cells formed by fusion of myoblasts. (fig 68)
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Sarcomere structure of myofibrils, dark=A band, light=I band
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X-sec of myofibril, insect flight muscle, verts slightly different.(Fig.70)
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-actinin
Sliding filament model (Fig.71)
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MT-based Motors: Kinesin & Dynein
Kinesin is a large protein with 4 polypeptide chains
Like myosin it has 2 heavy chains, each w a globular head domain and long -helical tail.
2 light chainson cargo-
MT binding endbinding (vary in diff.
cells w diff.cargo)
ATP-binding site Coiled-coilin each head tail
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Kinesins +
KIFs -(KinesinFamily +members
+
Freeze-Etched,ShadowedTEM
+ 2 HC in tail
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Comparison of kinesin and myosin mechanochemical cycles
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3. Dyneins are a family of minus end directed MT motors.Largest and fastest molecular motors (14 m/sec vs2 m/sec for kinesin)(fig 56)
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Dynein moves vesicles and the Golgi app toward the cell center.
A) Untreated B) NocodazoleFig. 62