Contractile Proteins Flashcards
Actin bundles
assembled via accessory proteins; cross linked into closely packed parallel arrays; Have POLARITY
Actin networks
loosely crosslinked in orthogonal arrays to form a 3D meshwork with gel-like properties
Actin-Bundling proteins
cross linking of F-actin achieved by polypeptides with at least two actin binding sites; typically small ridged proteins that force the filaments to align closely with each other
Closely spaced actin filaments in a bundle that are parallel; helps increase surface area
projections such as microvilli
Binds to actin filaments as a monomer, holding two parallel filaments CLOSE together
fimbrin
Reason for loosely bundled actin filaments; less cross linking
contraction; contractile rings in mitosis
binds to actin as a dimer; filaments are separated by a greater distance allowing motor protein (myosin) to interact during the contraction
alpha-actinin
holds actin filaments in networks together; binds actin as a dimer with binding locations on opposite ends; can create a 3D meshwork; maintains structure and function of membranes
filamin
Role of spectrin
binds to actin as tetramer forming an actin network on the cytoskeleton; interacts with ankyrin and protein 4.1
actin filaments crosslinked to 3D network that are key in phagocytosis
Pseudopodia
broad, sheet-like extensions of actin at leading edge of cell with actin network
Lamellipodia
thin membrane projections supported by actin BUNDLES; formation and retraction is based on assembly/disassembly of the actin filaments
Filopodia
How does myosin move along actin filaments
ATP hydrolysis
Myosin head
ATP binding and ATPase; actin binding
Myosin neck
flexible, binds myosin light chain peptides
Myosin Tail
intertwine to bring myosin head regions together and bind membranes/organelles
Class I myosin
membrane association and endocytosis
Myosin II class
contraction of muscles
Class V myosin
organelle transport
Myosin pathway
binding of ATP causes actin release; binding of actin again causes release of Pi to drive the power stroke, moving the actin filament; remains bound til ADP/ATP switch
Smooth muscle contractions
myosin folds over itself (no troponin etc.) when low Ca2+; when Ca2+ goes up, myosin light chain kinase is activated which phosphorylates myosin light chain; myosin can then unfold and interact with actin
Non muscle contractions
several actin-myosin structures similar to skeletal; cytokinesis has bundles of F-actin and myosin II forming contractile ring; movement along ring creates the cleavage furrow
cell migration
actin at leading edge (lamellipodia) moves forward and extends projections by adding actin to plus end
