Pg.1010-1022.docx

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10 Apr 2012
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Pg.1010-1022
Molecular Motors
Motor Proteins: bind to cytoskeleton filament and move along
actin/microtubule
They carry “cargo” and differ in the direction that they are moving
Motor proteins can carry membrane enclosed organelles such as
mitochondrion, vesicles and Golgi stacks
Move unidirectional
The motor proteins interact with filaments using their heads and hydrolyzes
ATP
Actin-based Motor Proteins are members of the Myosin Superfamily
Myosin: generates force for muscle contraction
Ex. Myosin II: two heavy chains and two light chains; long amino acid
sequence
Each myosin head binds and hydrolyzes ATP
Many different types of myosin were discovered
All myosin move to the plus end of the actin filament except myosin VI
There are Two Types of Microtubules Motor Protein: Kinesin and Dyneins
Kinesin: motor protein that moves along microtubules
Identified first in the axon of a squid
Has two heavy chains and two light chains
Most walk towards the plus end of the microtubule
Many different types of kinesin
Dynesin: minus end directed proteins of microtubules
2 or 3 chains that vary in combination of light and dark chains
Largest known molecular proteins
Fast
The Structural Evolution of Myosin and Kinesin Indicates a Common Evolutionary
Origin
Structure of Myosin and Kinesin show signs of evolutionary origin
Motor Proteins Generate Force by Coupling ATP hydrolysis to Conformation
Motor proteins use ATP to push along the microfilaments
Ex. In actin there is a lever arm in which ATP can bind
There is a change in conformation for the motor protein
The release of a phosphate triggers a power stroke where the motor protein
moves forward
In kinesin the same process occurs expect with two heads, this creates a
walking motor protein
The position of the end determines the direction towards the plus or minus
end
Dynesin is structurally unrelated to myosin and kinesin
Head has 6 AAA domains and a heavy chain c-terminus
“power stroke” is determined by the release of ADP
Motor Protein Kinetics are Adapted cell function
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