Mammalian Cell Activity:
               Chromosomes move to poles;       Flagella wiggle to move sperm;
               Cilia beat to move mucus;          Synaptic vesicle move to release transmitters.


 
Molecular Motors...
        any protein that convert
       
ATP hydrolysis into a
        produce a physical force or torque.

              


 
> 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 ]


  > 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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 3 Classes of Motor Proteins in Mammalian Cells:      
     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


  

 
 

 

 

                              
 

 

> the motility cycle was described in 2000 by R.D. Vale and R.A. Milligan
                                 Science 288: 5463: 88-95, April 2000

 

> 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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