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CONTACT INFORMATION: LUISA IRUELA-ARISPE MBI/BOYER HALL 559 PHONE# 310 - 794-5763

CYTOSKELETON Lecture 4 January 18th, 2005. CONTACT INFORMATION: LUISA IRUELA-ARISPE MBI/BOYER HALL 559 PHONE# 310 - 794-5763 arispe@mbi.ucla.edu. CYTOSKELETON. STRUCTURAL FRAMEWORK OF THE CELL: IT CONSISTS OF FILAMENTOUS COMPONENTS. ACCORDING TO THEIR SIZE, CYTOSKELETAL FILAMENTS ARE

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CONTACT INFORMATION: LUISA IRUELA-ARISPE MBI/BOYER HALL 559 PHONE# 310 - 794-5763

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  1. CYTOSKELETON Lecture 4 January 18th, 2005 CONTACT INFORMATION: LUISA IRUELA-ARISPE MBI/BOYER HALL 559 PHONE# 310 - 794-5763 arispe@mbi.ucla.edu

  2. CYTOSKELETON STRUCTURAL FRAMEWORK OF THE CELL: IT CONSISTS OF FILAMENTOUS COMPONENTS. ACCORDING TO THEIR SIZE, CYTOSKELETAL FILAMENTS ARE CLASSIFIED INTO: 1) MICROTUBULES - 25nm 2) INTERMEDIATE FILAMENTS - 8-10nm 3) MICROFILAMENTS - 6nm

  3. Cytoskeleton - Major Functions Structure support Intracellular transport Contractility and Motility Spatial Organization Actin filaments Actin filaments Motor protein Intermediate filaments microtubule Nerve cell Motor protein Actin filaments microtubule microtubule Motor protein Epithelial cell Dividing cell

  4. Differential physical propertiesof cytoskeletal components Microfilaments Microtubules Intermediate Filaments

  5. THE CYTOSKELETON IS DYNAMIC

  6. MICROTUBULES CYLINDERS OF 24nm IN DIAMETER AND COMPOSED OF 13 PROTOFILAMENTS PROTOFILAMENTS ARE LINEAR POLYMERS OF TUBULIN. TUBULIN IS A 110KD HETERODIMER CONSISTING OF alpha AND beta - TUBULIN.

  7. MICROTUBULES GDP or GTP Always GTP Short, unstable Has orientation

  8. Microtubule Associated Proteins • MAPs can function as cross-bridges connecting microtubules. • They can affect microtubule rigidity and assembly rate.

  9. Tubulin molecule with bound GTP Protofilaments containing GDP tubulin are unstable and peel away from the microtubule wall GTP tubulin molecules add to end of microtubule Addition proceeds faster than GTP hydrolyses GDP tubulin is released to the cytosol Tubulin molecule with bound GDP GTP cape SHRINKING MICROTUBULE GROWING MICROTUBULE How do Microtubules Grow and Shrink?

  10. INTERMEDIATE FILAMENTS Keratin Filaments • Distribution of keratin on an epithelial cell by anti-keratin antibodies

  11. Monomer Intermediate Microfilaments Parallel heterodimer Intermediate filaments are mostly found in epithelial cells. Example: Keratins and Vimentins The provide the mechanical stability of cells. Antiparallel tetradimer protofilament protofibril Lateral association Intermediate filament

  12. Intermediate Anchored Filaments Adherens junction ankyrin actin Intermediate filaments microfilaments desmosome Actinadhesion plaque hemidesmosome Extracellular matrix Desmosome Hemidesmosome Plaque proteins integrin ECM cell

  13. Physical Resistance to Deformation is Provided by Intermediate Filaments

  14. MICROFILAMENTS (or Myofilaments) • PRESENT IN HIGHEST DENSITIES AT THE PERIPHERY OF THE CELL • MOSTLY CONSTITUTED OF ACTIN AND MYOSIN • INTERACTION OF ACTIN AND MYOSIN ENABLE CELL MIGRATION • POLYMERIZATION IS ATP-DEPENDENT

  15. F-ACTIN G-ACTIN

  16. sugar amoeba

  17. Barbed end Pointed end Pi D Css ADP ATP T Treadmilling T D T D D (-) (+) ADP-actin ATP-actin Steady state concentration Css Filament turnover Pure actin: 0.1 µM 3µm / 90 min Lamellipodium:? 3 µm / 1 min 2 µM

  18. Actin Depolymerizing Factor (ADF) / Cofilin: • Ubiquitous, conserved, stimulus-responsive regulators of actin dynamics in motile processes: • Embryonic development • Yeast endocytosis • Cytokinesis • Listeria propulsion • Localized in motile regions of cells (at the leading edge)

  19. x 30 ADF ADF D D T ADP ATP ADF increases the treadmilling of F-actin ADF binds F-ADP-Actin better than F-ATP-Actin T D D D T D Increase inCss => faster + end growth

  20. Profilin Actin filament Profilin increase the rate of actin-based motility

  21. x 30 ADF D ADF ADF T T D x125 ADP ATP D T D P Profilin Profilin Profilin Synergy between Profilin and ADF 2. Profilin transports actin-ATP to leading edge. 1. Profilin binding increases rate of actin-ADP to actin-ATP.

  22. Arp3 47 Arp2 42 21 20 34 40 16 Non-zero crosslink Two hybrid Zero-length crosslink The Arp2/3 complex: downstream target of multiple signaling pathways leading to actin assembly • Seven conserved subunits including Arp2 and Arp3. • Is activated at the surface of Listeria by the ActA protein to stimulate actin polymerization and bacterial propulsion. • Localizes at motile regions of cell. • Generates new actin filaments in a stimulus-responsive and spatially controlled fashion. ARP: Actin Related Protein. Has similar structure to actin.

  23. sugar amoeba

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