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

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Presentation Transcript
slide1

CYTOSKELETON

Lecture 4

January 18th, 2005

CONTACT INFORMATION:

LUISA IRUELA-ARISPE

MBI/BOYER HALL 559

PHONE# 310 - 794-5763

[email protected]

slide2

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

cytoskeleton major functions
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

differential physical properties of cytoskeletal components
Differential physical propertiesof cytoskeletal components

Microfilaments Microtubules Intermediate

Filaments

slide6

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.

slide7

MICROTUBULES

GDP or GTP

Always GTP

Short, unstable

Has orientation

slide8

Microtubule Associated Proteins

  • MAPs can function as cross-bridges connecting microtubules.
  • They can affect microtubule rigidity and assembly rate.
how do microtubules grow and shrink

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?
keratin filaments

INTERMEDIATE

FILAMENTS

Keratin Filaments
  • Distribution of keratin on an epithelial cell by anti-keratin antibodies
intermediate microfilaments

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

intermediate anchored filaments
Intermediate Anchored Filaments

Adherens

junction

ankyrin

actin

Intermediate

filaments

microfilaments

desmosome

Actinadhesion plaque

hemidesmosome

Extracellular matrix

Desmosome Hemidesmosome

Plaque

proteins

integrin

ECM

cell

slide14

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

slide15

F-ACTIN

G-ACTIN

slide16

sugar

amoeba

treadmilling

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

a ctin d epolymerizing f actor adf cofilin
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)
adf increases the treadmilling of f actin

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

synergy between profilin and adf

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.

the arp2 3 complex downstream target of multiple signaling pathways leading to actin assembly

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.

slide23

sugar

amoeba

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