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Up until this point we’ve spoken about the cytoskeleton, microtubules, and actin. Today we
will discuss the cytoskeletal motors, this is involved in every function of the cell i.e.
movement.
Myosin – The actin Motor Protein
All motor proteins are enzymes, they harness energy within ATP and use it to produce force
and work on the filaments. Because of this they are known as mechanochemical enzymes.
Myosin’s were discovered in the muscle tissue, these are the cytoskeletal arrays, stacked on
top of one another and interconnected with myosin’s. Researchers now know there are
different myosin’s within the body that do different tasks.
What are they?
Myosin’s are a family of proteins that can use the energy released by the hydrolysis of ATP
to move.
All myosin has the same basic structure: a head, neck, and tail.
1. Head- shown as a cleft (cut out) this binds to the actin filaments and ATP to release
the energy into the molecule.
2. Neck – This takes the energy and applies it to an actin fiber. It determines how much
force a myosin will be able to produce and when. There are two different proteins that
are regulated by calcium. In this case myosin can be regulated by other molecules.
3. Tail – The head comes through the neck into the tail. This is a dimer – two proteins
wrapped around one another to form a tail. These functionalise the myosin. Each tail
will have a different task, i.e. binding to other myosin’s to bundle them together and
apply more force. The tail varies in length and function depending on the nature of
the task.
Cartoon representation of the crystal structure of S1 Myosin head domain.
o Actin binding site – this is where the molecule will dock with the actin filament.
o Nucleotide binding side – uses ATP to release energy.
o Essential light chains – low molecular rate. There are carmodulin like proteins.
Different types of Myosin’s – additional material available on Moodle.
Class 1 – a single molecule decorated with accessory proteins. It can stretch to 10-14 nm
and applies force to the + end of the actin filament. This molecule binds to the actin filament,
1
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