talbot actin

Question 1

• Cell Crawling: role of actin filaments and ABPs

Answer 1

o Nucleating proteins promote pushing out actin filaments towards leading edge structures.
o Bundling proteins in filopodia help form exploratory fibers.
o Integrins* form new adhesion point; severing proteins promote depolymerization of actin filaments.
o Myosins walk along actin filaments (stress fibers), pulling rear of cell towards new adhesion point.

Question 2

Myosin subfamilies

Answer 2

Myosin I: found in all/most eukaryotic cells. Monomeric myosin with a single ATPase head and tail (cargo binding domain). The ATPase head interacts w/ the actin filament, moving along the filament as ATP is hydrolyzed. (move toward the + end of the actin filament)
can have plasma membrane as their “cargo”. contract and plasma membrane gets closer to + end

Myosin II:• Myosin II subfamily: “muscle” myosins (but can be found in non-muscle cells as well, just most abundant in muscle). Two subunits interact to form a structurally polar homodimer with the tails forming a coiled-coil. In skeletal (and cardiac) muscle, clusters of homodimers interact to form the structurally bi-polar thick myosin filament.
increase the overlap of the 2 actin filaments
• Bipolar means that that one end of the structurally polar units are exposed at either end while the other end of the structurally polar unit are all oriented towards the middle.
o The N-terminus (ATP hydrolyzing “feet”) of each myosin subunit is found at either end of the thick filament.
o The C-terminus of each myosin subunit is oriented towards the center of the thick filament.

actin overlap==> contraction

lots of subfamilies with highly conserved motor domains (N-terminal amino acid sequence) where bind actin and hydrolyze ATP

Question 3

Muscular dystrophy

Answer 3

dystrophin is an ABP that helps link muscle cytoplasmic cortical actin to the plasma membrane (and, indirectly, the extracellular matrix); non-functional dystrophin destabilizes complex and leads to muscle necrosis