Molecular & Cell Biology

S. Rahgozar,PhD

University of Isfahan

Faculty of Science

6. Cytoskeleton and Cell Movement

6.2. Actin /myosin & Intermediate Filaments

1392-93

(2.3 μm)

Actin-myosin complex in muscle Fibers

The additional proteins are titin and nebulin

A number of different types of actin binding proteins remodel

or modify existing filaments.

o Muscle Contraction

Sliding filament model of muscle contraction

Myosin II molecule

(catalytic core) (Lever arm)

+

Model for myosin action

Association of

tropomyosin and

troponins with

actin filaments in

striated muscles

After calcium release Before calcium release

Examples

Stress fibers

Adhesion belts in epithelial cells

Contractile ring

Actin-myosin complex in

Non muscle Fibers

1- Myosin II

Contractile assemblies of actin and myosin in non muscle cells

Regulation of Myosin II

MLCK: Myosin light-chain kinase

2- Myosin I

3- Myosin V

Formation of cell protrusions and cell movement

o Crawling of amoebas

o Migration of embryonic cells

during development

o Invasion of tissues by white blood

cells during infections

o Migration of cells involved in wound healing

o Spread of cancer cells during the metastasis of malignant tumors

o Phagocytosis

o Extension of nerve cells during development of the nervous system

Examples

Actin filament branching at the leading edge

Intracellular organization of

keratin filaments

Intermediate Filaments

Actin filaments’ diameter: 7 nm

Microtubules’ diameter: 25 nm

Intermediate filaments’ diameter: 8-11 nm

Assembly of intermediate filaments

Keratin fillaments attached to the dense plaques of intracellular protein on both sides of a

desmosome

Desmosomal cadherins (desmoglein and desmocollin) link adjoining cells to

intermediate filaments through plakogobin, plakophilin and desmoplakin

Various cell junctions found in a vertebrate epithelial cell

Small intestine of a vertebrate