1. 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

2. All myosins have head(s), neck and tails 13 family members in humans But know Myosin I, II, and V Head has ATPase and actin binding domains, actin accelerates ATPase Neck regulates the head, light chains bind calcium Tails have specific binding sites Gentle digestion releases domains

3. Myosin II

4. Experimental tools for your toolbox: Sliding filament assay, Optical trap ATP requirement, conditions, direction, rates, force movement in discrete steps (cog wheel)

8. Know the contraction cycle!! 1.No ATP- rigor state 2.ATP causes release and movement 3.ATP hydrolysis allows rebinding 4.Loss of Pi causes power stroke 5.ADP release restores to rigor position

9. 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

16. Tropomyosin, ropelike protein binds actin. Troponin, binds TM and calcium Calcium binding nudges TM TM movement exposes myosin site on actin With myosin able to bind, the contraction cycle proceeds

17. Smooth and skeletal contractions differ Instead of troponin, smooth muscles use caldesmon at low calcium Calcium levels change more slowly The network is less ordered.

18. Caldesmon binds Caldesmon off by CaM Additional control by kinases

19. It’s also possible to control contraction by myosin modification Examples: 1. Invertebrate muscle, calcium binding to myosin LC 2. Vertebrate smooth muscle, phosphorylation of myosin LC by MLCK in a Ca++/CM cycle 3. Or by Rho kinase These pathways are independent of the action potential. They represent other signaling pathways.