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
        physical force or torque.

               


  > includes:    1.  ATPases that transport ions  [ NaK-ATPase  & H+ATPase ]
                      2.  enzymes that unwind DNA, etc..   [ helicase - DNA gyrase & topoisomerases ]
            and     3.  proteins that move vesicles along cytoskeleton [ dyneins & kinesins ]


  > Function:    some intracellular "motors" function via ATP hydrolysis,
                        which produces a conformational shift in a globular domain that can
                        allow a "walking*" movement of organelles along a cytoskeletal filament.
  

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 3 Classes of Motor Proteins involved with cellular structure & transport:      
     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,                   
  BACK                             chromosome alignment and cytokenesis


  
 
 

 

 

                              
 

 

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

> 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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