Final: Ch 17 Actin Filament Assembly, Cell Structures Flashcards
the rate-limiting step of actin polymerization is what
formation of the actin nucleus that a filament grows from
used as a regulation point
2 major classes of actin nucleating proteins are
the formin protein family, and the Arp 2/3 complex
controlled by signal transduction pathways
formins lead to the assembly of _____ actin filaments, whereas the Arp2/3 complex leads to _______ networks
long, branched
2 important domains of formins
FH1 and FH2 domains
bind actin subunits (FH2) and block CAP protein
increase concentration of profilin-ATP-G-actin complexes (FH1)
how is formin regulated
membrane bound Rho-GTPase
when it is switched from Rho-GDP –> Rho-GTP, it binds and activates formin
formins assemble long actin filaments like….
stress fibers
filopodia
contractile ring
Arp2/3 interacts with what to become a nucleator
nucleation promoting factor (NPF)
allows Arp2 and Arp3 to change into the correct conformation
binds branch at 70 degrees to side of actin filament
intracellular movements can be powered by _____ __________
actin polymerization
b/c ATP hydrolysis
intracellular bacterial parasite Listeria monocytogenes
food-borne parasite that causes mild GI problems
to move from one host cell to another it polymerizes actin into a comet tail
when it reaches the membrane, it pushes itself inside
how does Listeria polymerize actin
has a surface protein called ActA that mimics a NPF to activate Arp2/3
actin assembly powers what type of endocytosis
fluid-phase
endocytosis assembly factors recruit __s so as the endocytic vesicles invaginate, they are propelled into the cytoplasm
NFPs
causes a short-burst of actin polymerization using the Arp2/3 complex
phagocytosis
WBC engulf pathogens
uses microfilaments and myosin motor proteins to draw the pathogen into the cell
fungi and sponges have toxins that target the polymerization cycle of actin…one class increases the monomer pool
cytochalasin D - depolymerizes actin by binding + end and blocking addition of monomers
latrunculin - binds G-actin to prevent its addition
class of toxins that shifts the monomer-polymer equilibrium in favor of filaments
jasplakinolide - stabilizes actin dimers
phalloidin - prevents F-actin only from depolymerization
____-____ proteins organize actin filaments into bundles or networks
cross-linking proteins
to be able to organize actin, an actin cross-linking protein must have two…
F-actin binding sites
fimbrin
a cross-linking protein w/ 2 actin binding sites found in microvilli that builds bundles of actin filaments with the same polarity
found in microvilli, filopodia, focal adhesions
a dimeric cross-linking protein has what
1 actin binding site
2 chains associated into dimers that bring 2 actin binding sites together
alpha-actinin
a dimeric cross-linking protein that forms a rigid rod connecting two binding sites
found in stress fibers, filopodia, muscle Z lines
spectrin
cross-linking protein found in the cell cortex of RBC
makes networks under the plasma membrane to hold cell together during transport
anemia if mutation (low O2 delivery)
filamin
cross-linking protein with a flexible region that makes stabilizing cross-links between filaments in a mesh
found in the leading edge, stress fibers, filopodia
the Arp2/3 complex is also an important _____-_____ protein
cross-linking protein
binds the - end of one filament to the side of another filament
_____ proteins link actin filaments to membranes
adaptor proteins
ex. in RBC
how do RBC survive pumping by the heart, flowing through arteries, and squeezing through capillaries
a microfilament based network with tensile strength and flexibility
based on short actin filaments stabilized on their sides by tropomyosin and the capping protein tropomodulin (-) end
mutations in which proteins cause anemia in humans
spectrin
band 4.1
ankyrin
what is the orientation of actin filaments in microvilli
+ end at the tip
adherens junctions
specialized regions of the plasma membrane where epithelial cells contact each other
focal adhesions
specialized regions that mediate attachment of cells to the ECM
dystrophin
a protein that links the cortical actin network of muscle cells to the ECM
absence causes muscular dystrophy
what is the purpose of cross-linking actin filaments
structural support - holds cell together
