Contractile Proteins Flashcards
What are the 2 general types of actin structures?
actin bundles = parallel arrays, filaments have same polarity
actin networks = orthogonal arrays, mesh
What type of actin structure supports projections of the PM (microvilli)?
closely spaced actin filaments in parallel
What characterizes actin-bundling proteins?
cross-link F-actin w/ at least 2 actin-binding sites
size and shape of protein determines how actin associates (loose or tight)
What is fimbrin?
actin-bundling protein
holds 2 parallel filaments close together
What are contractile bundles?
loose bundles of actin filaments
give room for myosin to associate w/ actin
What is actinin
cross-linking protein for actin in loose bundles
binds as a dimer
What is filamin?
actin-bundling protein that holds actin in networks - can be 3D
binds as dimer
actin binding domains on opposite ends of dimer
What is spectrin?
tetramer that associates with actin in erythrocytes –> interacts w/ membrane proteins via ankyrin and protein 4.1
What is hereditary spherocytosis?
mutation in cytoskeleton proteins in RBCs (spectrin, ankyrin, 4.1) –> defective anchor pts –> membrane peels off and cell becomes spherical –> anemia
What are pseudopodia?
actin filaments cross-linked in 3D network –> phagocytosis
What are lamellipodia?
broad, sheet like extensions at leading edge of cell
made of network of actin filaments
What are filopodia?
Thin projections of PM supported by actin bundles
What characterizes the myosin superfamily?
all motor proteins
20 diff types
all move along actin via ATP hydrolysis
What characterizes myosin II?
in skeletal muscle
bipolar filaments
tails associate to form shaft
heads exposed
What are the 3 major domains of myosin?
Head
neck
tail
What is on the head of myosin?
actin binding sites
ATP binding sites
ATPase activity
What is on the neck of myosin?
flexible
binds myosin light chain peptides
What is on the tail of myosin?
intertwine to bring head regions close together
bind membrane/organelles
What is type I myosin used for?
What is its step size
membrane association, endocytosis
10-14 nm
What is type V myosin used for?
What is its step size?
organelle transport 36 nm (largest)
What is the basic mechanism of myosin moving along actin?
w/out ATP, myosin bound to actin –> bind ATP –> conformational change –> release actin = head cocked –> binds actin and release ATP –> power stroke = movement
How does the size of neck of myosin relate to rate of movement along actin?
longer neck domain –> increased velosity
What is the step size of myosin II?
8 nm (smallest = shortest neck)
What end of actin does myosin move toward?
plus end of actin
What end of actin is attached to the z disk?
What end of actin is closer to the m band?
+ end on z disk
- end at M band
How are actin and myosin arranged in smooth muscle?
loosely arranged around periphery, held in place by protein dense bodies
In smooth and non-muscle cells, what is myosin’s “relaxed” state?
folded and inactive
when there is low calcium
In a smooth or non-muscle cell, what does an increase in calcium trigger?
CaM + MLC kinase to become active –> myosin unfolds and becomes active –> contraction myosin filament assembled
what is the contractile ring?
what splits cells in cytokinesis
made of bundles of f-actin and myosin II
How is vesicular transport accomplished?
myosin V is folded and inactive –> binds cargo –> straight and active –> carries vesicle through cell by moving along actin
At what end of actin is there growth?
plus end
minues end = shrinkage
What is important w/ focal adhesions in cell migration?
actin must pull adhesion off basement membrane to move cell
What is duchene muscular dystrophy caused by?
x-linked recessive mutation of dystrophin gene
out of frame mutation
What is becker muscular dystrophy? what is it caused by?
milder form of duchene
x-linked recessive, in-frame mutation of dystrophin gene
What is the dystrophin protein?
rod-like protein that connects cytoskeleton to basal lamina and stabilize membrane
helps stabilize cell during muscle contraction; w/out it –> damage to muscles
What is special about the dystrophin gene?
largest human gene known
