Motor Proteins Flashcards
Cytoskeletal motor proteins associate with their filament tracks through
a “head” region, or motor domain, that binds and hydrolyzed ATP to drive conformational changes as it “walks” along the filament.
What does the regions of filament determine
The head determines the filament and direction of movement, while the tail determines the cargo.
Groups of cytoskeletal motor proteins
-myosins
-kinesins
-dyneins
First motor protein identified and involved in muscle contraction
Myosin II (a signal myosin motor)
Myosin II structure
C terminal tail that is associated with the cargo, we have 2 coils of alpha helices, we also have an N terminal region head region
Each myosin head binds and hydrolyzes ATP to walk toward the _____ end of an actin filament
plus
What myosin doesnt move toward the plus end of actin
Myosin IV
Myosin V role
involved in vesicle and organelle transport
role of Myosin I
involved in intracellular organization including the protrusions of actin-rich structures at the cell surface (microvilli)
role Myosin II
involved in muscle and non-muscle cell contraction and cytokinesis.
Two types of microtubule motor proteins
-kinesin
-dyenins
Similarities between kinesin and myosin II
have 2 heavy chains and 2 light chains per active motor (2 globular head motor domains and an elongate tail for heavy chain dimerization)
Most kinesins have a binding site in the tail for either a ___________or another ________
-membrane-enclosed organelle or another microtubule
Motor proteins differ in (3)
-the type of filament they associate with
-the direction they move
-the cargo they carry
Kinesin 1 structure
has the globular motor heads that will walk along the MT at the N terminal, it is coiled into a dimer and has a c terminal end which will bind to the cargo
What is the “cargo”
the cargo is usually organelles that need to move within the cell, a big one is mitochondria
Kinesin 3 structure and involved in what
Looks very different, exists as a monomer and is also involved in moving organells around the cell
Kinesin 5 structure and function
most similar to a myosin fiber, but it only forms this tetramer, but a long fiber (like myosin does), it has a similar function to myosin in that it is responsible for sliding one MT relative to another MT generating tension
Kinesin 13 structure and function
actually has the motor domain in the middle (not on the N terminal like the rest) and it is thought to play a role in catastrophe but we don’t really know how it does this.
Which kinesin has motor domain in middle
13
Dyneins
a family of minus-end microtubule motors unrelated to kinesin superfamily
Two major braches of dyneins
1) cytoplasmic dyneins
2)axonemal dyneins
What are cytoplansmic dyneins
heavy chain homodimers with two large motor proteins as heads
What are axonemal dyneins
heterodimers and heterotrimers with 2 or 3 motor proteins as heads.
What are cytoplasmic dyneins involved in
vesicular trafficking and Golgi apparatus positioning (therefore MTOC positioning as well)
What are axonemal dyneins involved in
the beating of flagella and cilia
What are the largest and fastest molecular motors
Axonemal dyneins
Are the motor domains of myosin or kinesins substantially larger
Myosins
Differences between myosins and kinesins
These two motors track along different filaments, have different kinetic properties and no detectable a.a. similarities