Contraction, Locomotion (Ch 16), Shelden

Transcription

1 Contraction, Locomotion (Ch 16), Shelden 1 Molec Biol Cell 5 th ed. Supplemental Videos Actin-dependent ATP hydrolysis by myosin generates motile force

2 The Myosin ATPase activity cycle 2 ATP binding releases myosin from actin (rigor is caused by lack of ATP) ATP hydrolysis to ADP+Pi moves myosin forward Release of Pi accompanies reattachment of myosin to a new actin subunit Release of ADP causes force generation and movement Fig 16-61

3 The Myosin ATPase activity cycle 3 Molec Biol Cell 5 th ed. Supplemental Videos

4 Different Myosins Exhibit Different Motile Behaviors 4 All myosins except myosin VI move toward the plus end of actin filaments Fig 16-57

5 5 Contractile force is generated in all types of cells by the action of bipolar myosin II thick filaments Fig Fig 16-55

6 Smooth muscle cells (and non-muscle cells) assemble myosin thick filaments as needed by regulating myosin light chains 6 Fig 16-72

7 Myosin thick filaments assemble during smooth muscle cell contraction and apply force to preassembled actin filaments 7 Anti alpha actinin Actin filaments are attached to the cell membrane at dense plaques containing alpha actinin and other actin associated proteins. Fujiwara et al., J. Cell Biol (1983) 96:

8 Isolated smooth muscle cell contraction 8 relaxed formation of myosin thick filaments contraction Driska et al., Journal of Applied Physiology, Vol. 86, Issue 1, , January 1999

9 Formation of skeletal (striated) muscle 9 Skeletal muscle myotube Showing nuclei Myotube formation from myoblasts

10 Fig Skeletal muscle cells contain thick filaments organized into permanent sarcomeres Fig I-band A-band

11 Sarcomeres are highly ordered structures 11 Actin thin filament length is determined by nebulin The plus ends of actin are attached to Z discs and capped by CapZ Minus ends of actin are protected by tropomodulin Thick filaments are positioned by titin Fig Fig 16-76

12 12 Thick and thin filaments slide past each other during contraction, but don t change length. Fig 16-76

13 Regulation of sarcomere contraction 13 Neuromuscular junctions Fig Nerve impulses cause release of acetylcholine at the junction. Binding of acetylchline to the muscle cells opens ion changels that lead to depolarization of the plasma membrane (sarcolema) and transverse tubules

14 Depolarization of the tranverse tubules stimulates release of calcium from the sarcoplasmic reticulum (a modified ER) into the cytoplasm 14 Fig 16-77

15 Calcium binds to the troponin complex and causes attached tropomyosin to move away from actin 15 Troponin C: binds calcium Troponin T: attaches tropomyosin Troponin I: inhibits myosin activity by changing shape Myosin binding sites on actin are revealed by movement of tropomyosin Fig 16-78

16 Smooth and Striated Muscle 16 Cells Smooth Individual cells Striated Multicellular syncitia (skeletal) Actin Actin meshwork anchored in dense plaques by alpha-actinin. Myosin not assembled when relaxed. Actin bundles anchored in Z lines using alpha-actinin. Myosin assembled in thick filaments. Organiz ation Simple cell architecture Myofibrils with M-lines, Z-lines, A bands, I bands. Transverse tubules and sarcoplasmic reticulum Trigger Contraction initiated by activation of myosin light chain kinase, causes mini-myosin filaments to form Neurons depolarize sarcolema. Depolarization enters T-tubule system, causing calcium release from sarcoplasmic reticulum. Calcium binds to Troponin complex, moving tropomyosin out of the myosin binding site on actin filaments.

17 Movement of cells involves protrusion, attachment, transport of the cell components and retraction of trailing attachments. 17 Fig 16-86

18 Amoeboid cell movement 18 Molec Biol Cell 5 th ed. Supplemental Videos

19 Keratocyte movie 19 Rachael Ream, George Somero & Julie Theriot.

20 20 Membrane protrusion is driven by actin polymerization Lysteria movement (J. Theroit, Ph.D.)

21 Cell Locomotion 21 Lysteria movement (J. Theroit, Ph.D.)

22 Protrusion 22 Lamellar (and pseudopod) protrusion of the plasma membrane is driven by cyclical actin polymerization at the cell periphery and depolymerization in more interior sites Cofilin prefers ADP actin

23 23 Attachment is mediated by formation of focal adhesions Elements of Focal Adhesions: 1. Transmembrane proteins (integrins) 2. Regulatory elements 3. Coupling proteins talin and vinculin 4. Actin Fig 19-45

24 Crawling movement of fibroblasts 24 Copyright Eric Shelden

25 Focal adhesions in a moving 25 fibroblast Bhatt et al., Journal of Cell Science 115, (2002)

26 26 Forward transport of organelles is mediated by motor proteins (myosins, dyneins and kinesins) Wu et al., Cell Biol., Volume 143, Number 7, December 28, See also

27 Myosin II nulls Wild-type amoeba Retraction of trailing cellular attachments is mediated by myosin II-dependent contraction at the rear of cells 27 David Knecht, University of Connecticut Fig (Video on next slide) Myosin I (green) and Myosin II (red) in a motile cell

28 Video