Mammalian
Cell Activity:
Chromosomes move to poles; Flagella
wiggle to move sperm;
Cilia beat to move mucus;
Synaptic vesicle move to release transmitters. |
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Molecular
Motors...
any protein that convert
ATP hydrolysis
into a
physical
force or torque.
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includes: 1.
ATPases that
transport ions [
NaK-ATPase
& H+ATPase
]
2. enzymes that unwind DNA, etc.. [
helicases, gyrases,
topoisomerases
]
and 3. proteins that move vesicles along cytoskeleton [
dyneins &
kinesins ]
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Function: these intracellular "motors"
function via ATP hydrolysis,
which produces a conformational shift in a globular
domain that
can allow a "walking" movement along a cytoskeletal filament |
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Classes of Motor Proteins in Mammalian Cells:
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all are homo-dimers:
each has a foot that
attaches it to cargo;
have region that
hydrolyzes ATP;
and a stalk to hold dimer
to cargo |
click |
a. myosins - thick filaments travel
along (pull) thin actin filaments
18 subclasses - move distances with step of ≈
37nm |
b. kinesins - travel along microtubules
15 families of proteins - long range from near nucleus to cell periphery
average step ≈ 8.3nm
EX:
vesicles of neurotransmitters move from cell body
along axon to synaptic knob |
c. dyneins -
walks along MT's - move from periphery to near nucleus
multi-subunit complex with ≈ 8.9nm step
connect MT's in
cilia &
flagella helping them bend in unison
dyneins & kinesins also help
spindle assembly,
next
chromosome alignment and cytokensis |
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the motility cycle
was described in 2000 by R.D. Vale and R.A. Milligan
Science 288: 5463: 88-95, April 2000
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Diseases of Motor Proteins:
missing myosins in cardiac muscle = adult onset
hypertrophic myopathy
myosin V mutations = coat color changes
(lack of melanocyte vesicle transport)
myosin VI mutation (controls stereocilia of ear hair cells) =
deafness
defective dyneins = retrograde axonal transport & neurodegenerative
diseases as ALS. |
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