Cytoskeleton III Chapter 16. Actin binds to many different proteins.

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Presentation transcript:

Cytoskeleton III Chapter 16

Actin binds to many different proteins

Plectin (green) crosslinks intermediate filaments (blue) and microtubules (red)‏

Cross linking proteins organize different assemblies of actin filaments actin binding sites in red

Actin bundles in a microvillus

Filamin crosslinks actin into 3-dimensional networks with gel-like properties

Melanoma cells with low filamin levels crawl poorly and tend not to metastasize

When filamin levels are restored the cells move normally and become highly metastatic

Three stages in control of bleeding

Severing existing actin filaments can accelerate assembly of new filaments

Gelsolin severs actin filaments

Actin filament dynamics and platelet activation

Platelets prior to activation

Activated platelet with large spread lamellipodium

Activated platelet after contraction

Aggregation of platelets

Thrombin is produced at cell surface of platelets

Ca 2+ and diacylglycerol activate protein kinase C

Fibrin emerging from clump of activated platelets

ERM proteins attach actin to plasma membrane

Actin fibers often terminate at focal points

Extracellular signals can effect actin organization, vinuculin identifies focal contacts

Extracellular signals can effect actin organization

Structure of myosin II Myosin head binds and hydrolyzes ATP

Electron micrograph of myosin molecules

Myosin is arranged in thick filaments

Myosin heads are on outside of thick filament

Motor activity is contained completely within myosin heads

Myosin heads can move actin filaments Speed of 4 micrometer per sec

Attached, no ATP Rigor configuration, state acquired during rigor mortis

ATP binding causes release of actin filament

Hydrolysis of ATP causes displacement of head by 5 nm

Release of P i causes tight binding to new position on actin filament

ADP is released and rigor configuration is assumed once again

Mechanochemical cycle of myosin

DVD clip 74