actin Flashcards
what are actin filaments?
microfilaments - helical polymers of protein actin
what are actin subunits?
called globular or G-actin
a polypeptide carry8ing ATP or ADP
what does actin assembly provide?
polarity to the filament (- end = atp-binding pocket exposed, + end = atp-binding pocket is buried
where does growth happen in actin?
in the + end mostly
what purpose does nucleation have?
is it the rate-limiting step in formation of actin filaments
what affect does numner of actin molecules bonding have?
two molecules are a weak bond, three is more stable
what is phalloidin?
drug that stabalizes F-actin
what are filopodia and lamellipodia?
protrusive structures made by migrating cells
what do actin-binding proteins do?
regulate polymerization and length of filaments
where do capping proteins bind?
to the + ends of actin
what does cofilin do?
cuts actin filaments into small pieces
what does actin crosslinking makes?
complex structures such as filopodia and lamellipodium
what is alpha-actinin?
a crosslinking protein that makes F-actin bundles (a rigid dimer)
what is filamin?
a flexible actin crosslinker protein (flexible dimer)
what is the Arp2/3 complex?
made of 7 subunits similar to G-actin
promotes actin branching by binding to the side of ta filament and recruiting actin monomers
what are ERM proteins?
link actin cytoskeleton to membrane
Erzin, Radizin, Moesin (ERM)
what do cells change to assemble complex actin structures?
activity and localization of actin-binding proteins
what are filopodia used for?
probe environment for clues in migrating cells
what are Rho Rac and Cdc42?
small GTPases (signal formation of actin strucutres)
what family are actin-based motor proteins?
myosin superfamily
what do all mysosins share/differ?
similar motor domains
C-terminal tails are different (can be conventional or unconventional)
what do myosin heads do?
bind and hydrolyze ATP to walk towards + end of actin
what is myosin V?
two-headed molecule that that walks along actin to transport/disperse cargo
what is mysoin 1?
one head, binds membranes
what are the parts of myosin 1?
tail - binding (anionic phospholipid, protein cargo, phosphoinositide)
LCBD (arm) - regulates Ca, force, binds CaM chains
motor - forge and ATP generation, regulated by tropomyosin
what are myosin 1 mutants?
left/right inverted
what does myosin II do?
forms bipolar filaments
what do myosin light chains do?
they are regulatory subunits of myosin II
what does MLCK do?
phosphorylates the myosin light chains and unfolds myosin II into active state
what are stress fibers?
contractile actin bundles found in non-muscle cells (composed of actin filaments and non-muslce myosin II)
what is a myosin power stroke?
ATP binds to myosin head -> release of actin -> conformation shift in lever arm -> actin releases phosphate (power stroke generates force) ->myosin head and actin bound
