Date post: | 19-Dec-2015 |
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Myosin is a motor that runs along (or tugs at) actin.
Actin-based movement of vesicles
Chromosome migration
Myosin-driven cell shape changes
Muscle contraction
All myosins have head(s), neck andtails
13 family members in humansBut know Myosin I, II, and V
Head has ATPase and actin bindingdomains, actin accelerates ATPase
Neck regulates the head, lightchains bind calcium
Tails have specific binding sites
Gentle digestion releases domains
Experimental tools for your toolbox:
Sliding filament assay, Optical trap
ATP requirement, conditions, direction, rates, forcemovement in discrete steps (cog wheel)
Know the contraction cycle!!
1. No ATP- rigor state2. ATP causes release and movement3. ATP hydrolysis allows rebinding4. Loss of Pi causes power stroke5. ADP release restores to rigor position
The myosin-actin interaction drives muscle contraction
Muscles have the power of a car on a per mass basis
Skeletal, isotonic contractions
Smooth, isometric contraction
Tropomyosin, ropelike proteinbinds actin.
Troponin, binds TM and calciumCalcium binding nudges TM
TM movement exposes myosin site on actin
With myosin able to bind, thecontraction cycle proceeds
Smooth and skeletal contractions differ
Instead of troponin, smooth muscles use caldesmon at low calciumCalcium levels change more slowlyThe network is less ordered.
It’s also possible to control contraction by myosin modification
Examples:1. Invertebrate muscle, calcium binding to myosin LC2. Vertebrate smooth muscle, phosphorylation of myosin LC by MLCK in a Ca++/CM cycle3. Or by Rho kinase
These pathways are independent of the action potential. They represent other signaling pathways.