Cytoskeletal Structural Proteins Polypeptide types: Actin a microfilaments (70 Å diameter), Keratin an intermediate filament (100 Å diameter) Tubulin a microtubule (240 Å diameter)

Actin Microfilament Assembly F-actin (filamentous) and G-actin (globular) Polarity with ATP-binding end the negative (-) end Greater addition on the positive (+) end Single subunit

Microfilament Treadmilling

Crawling Cells via Microfilament Treadmilling Highly Dense Leading edge Upturned Leading edge

Cytoskeletal Structural Proteins Polypeptide types: Actin a microfilaments (70 Å diameter), Keratin an intermediate filament (100 Å diameter) Tubulin a microtubule (240 Å diameter)

Intermediate Filaments Basic structural unit: dimer of α-helices that wind around each other – coiled coil Includes soft keratins that define internal structures and hard keratins of skin, hair and claws Exclusively structural proteins Dead epidermal skin cells mostly keratin

Residue Arrangement in a Coiled Coil Structure Seven amino acid pseudo repeat with positions 1 and 4 hydrophobic residues Hydrophobic strip along the side of the helix

Intermediate Filament Dimer Model Human hair

Special Intermediate Filament for Large Animals: Collagen Triple helix extracellular matrix Holds cells, organs and bones together Rich in Gly (30%), Pro (30%) and hydroxyproline (30%)

Collagen Triple Helix Cross Section A narrow left-handed single helix but A right-handed triple helix

Collagen Single and Triple Helix Structure Pro drives the left handed configuration Only Gly can fit in the center position Reverse winding strengthens the helix

Lys Side Chain Cross Linking Collagen stronger than steel on a per weight basis

Cytoskeletal Structural Proteins Polypeptide types: Actin a microfilaments (70 Å diameter), Keratin an intermediate filament (100 Å diameter) Tubulin a microtubule (240 Å diameter)

Tubulin Forms Hollow Microtubules Tubular structure provides greater strength

β-Tubulin and Tubulin Dimer Describe the secondary structures of beta-tubulin. Guanosine nucleotide-sites with α-subunit site solvent inaccessible

Microtubules Function in Cell Division Draws chromosomes apart before cell division Polar structure that grows more rapidly at the (+) end Microtubule treadmilling can occur

Drug-Mediated Microtubule Depolymerization Colchicine binds between the alpha and beta subunits

Drug-Mediated Microtubule Polymerization Taxol stabilizes beta-tubulin subunits preventing depolymerization Blocks rapidly dividing cells such as tumor cells

Motor Protein Thick Filament Actin interacts with the thick filament of myosin causing muscle contraction Thick Filament

Myosin Head and Neck Region

Binding of ATP to Myosin Releases Myosin from Actin

ATP Hydrolysis Causes a myosin conformational shift and Increases myosin binding to actin Myosin binds to actin farther along the thin filament

Power Stroke Myosin binding to actin causes a release of phosphate and ADP

Chapter 5 Problems: 1, 3, 5, 7, 9, 11, 13, and 17, 20, 25, 51