Motor proteins belong to the group of cytoskeletal proteins. The cytoskeleton serves to stabilize the cell as well as its movement as well as the transport mechanisms in the cell.
What are motor proteins?
The group of cytoskeletal proteins is composed of motor proteins, regulatory proteins, Brϋck proteins, boundary proteins, and Gerϋst proteins. Motor proteins consist of a head domain and a tail domain. The head domain is also the motor domain. This serves to bind to the cytoskeleton to form a protein shaped structure. The motor domain contains the binding site fϋr the adenosine triphosphate (ATP) and the region of the protein that performs a specific movement upon a conformational change. The motor domain is highly conserved in each of the cytoskeletal protein subgroups, i.e., all proteins from the same subgroup have the motor domain constructed and functioning in the same way. The tail domain, on the other hand, binds to the respective target protein. It can also serve to allow multiple motor proteins to form a complex of proteins with each other.
Function, action, and tasks
The group of motor proteins is composed of kinesins, prestins, dyneins, and myosins. Kinesins generally form dimers, meaning they form protein complexes in pairs. These bind to the microtubules of the cell and move along these microtubules from the minus end towards the plus end, i.e. from the nucleus to the cell membrane. This movement along the microtubules transports organelles or vesicles from one location to another within the cell. Kinesin plays a role in neurotransmitter Ausschϋttung, in which vesicles containing neurotransmitter are transported along the microtubili to the presynaptic membrane. Kinesin is also involved in cell division. Similar to kinesin, dynein also forms dimers and binds to microtubules. However, these move from the plus to the minus end, i.e., from the cell membrane toward the nucleus. This is also called retrograde transport. Specific dyneins are found in the cell’s locomotion aids, such as cilia or geicles, which are also called flagella. These are found, for example, in spermatozoa. Myosin can also form dimers and binds to actin filaments. It moves from the minus to the plus end of the filaments and, like kinesin described earlier, serves to transport vesicles. However, the subtype Mysoin VI does not move in this direction. In addition, mysoin is found in increased amounts in muscle tissue together with actin in order to be able to carry out muscle contraction there. This occurs by pushing the actin filaments into each other. In addition, mysoin plays an essential role in endocytosis and exocytosis, as well as in the locomotion of the cell. This type of locomotion can occur in cells that do not possess flagella or cilia. Mysoin also has the peculiarity that it is found only in eukaryotes compared to dynein and kinesin, which are also found in prokaryotes. Prestin is found in the hair cells of the inner ear. Compared to the motor proteins described so far, prestin is regulated by electrical voltage, which fϋuels its mechanical movement to be carried out in the cell.
Formation, occurrence, properties, and optimal values
Motor proteins are allosteric proteins. These proteins change their conformation, or shape, after they bind a ligand. For example, this may be a receptor, such as the insulin receptor, which changes its confomration after binding from its ligand, insulin. This then results in the receptor triggering a signaling cascade. The motor proteins require adenosine triphosphate (ATP) fϋr their activity. They serve to generate cell movement but also transport within the cell such as endocytosis or exocytosis. This is the uptake or release of certain substances or proteins by the cell. An example is the delivery of neurotransmitters through the presynaptic terminal of a neuron by the fusion of vesicles containing the neurotransmitter and located in the cell with the plasma membrane of the neuron.
Diseases and disorders
If mutations occur in the gene that encodes fϋr the protein mysoin in the human body, this can lead to hypertrophic cardiomyopathy fϋ. It is a disease of the muscles of the heart. This type of disease is congenital. There is an uneven thickening of the muscles of the left ventricle.This is called hypertrophy. During exercise or other strenuous physical activity, the outflowing blood vessel of the left ventricle constricts. The heart muscles stiffen, which is described as compliancy disorder. The result is cardiac arrhythmia and shortness of breath. This disease is treated with medication, or the outflowing blood vessel of the left ventricle is relocated and muscle tissue is removed. Another disease is myoin storage myopathy. This is a clumping of mysoin in the muscle cells. As a result, the muscles become weak. The disease is usually diagnosed in childhood, but can also occur later in life. The weakening of the muscles fϋ results in a slowed gait and difficulty lifting the arms. In severe cases of this condition, there is also difficulty breathing. In addition, defects in muscular mysoin can also lead to the so-called Usher syndrome. This is a disease that causes deafness and blindness. A defect in the motor protein kinesin can lead to Charcot-Marie-Tooth disease, which is a form of muscular atrophy.