Molecular motor

Motor proteins are one of five functional groups of the cytoskeletal proteins in addition to the filamentous scaffold proteins that bridge proteins, proteins limiting and regulating proteins. They are distinct allosteric proteins that primarily serve under ATP consumption of movement generation, but partly also take control tasks. Mainly with these movements biological loads ( vesicles, organelles, etc.) transported or shifted against each other cytoskeletal elements.

Basic Structure

Motor proteins always consist of a so-called head (or motor domain ) and a tail domain.

Motor domain

Hereby, the protein binds to the Cytoskelettelement. In the motor domain also contains the ATP - binding site and the structures that perform the motion of the molecule in the conformational change. In the individual families of motor proteins, the motor domains are very uniform and highly conserved.

Tail domain

Here are the binding sites for the load to be transported. The structure of the tail domain also determines whether multiple proteins can assemble into larger complexes. The structure of the tail domain is highly variable.

Motor protein classes

• Kinesin: Binds to microtubules. Usually forms dimers. The direction of movement of kinesin is mostly from the negative to the positive end of the microtubule. It is primarily intended for the transport of organelles and vesicles. For example, vesicles are transported by means of kinesin neurotransmitters in nerve cells from the cell nucleus via the axon to the synapse. So it is in most cases a transport from the nucleus to the cell membrane. Kinesin also has important regulatory functions in cell division.
• Dynein: dyneins often form dimers and bind to microtubules. They move mostly from the plus to the minus end of a microtubule ( from the cell membrane to the nucleus ). There are special types of dynein, which occur in the axoneme of cilia and flagella.
• Myosin: myosin bind to actin filaments and can also be transported here as dimers vesicles or the like. Your direction is mostly from the negative to the positive end of a Aktinfilaments (except myosin VI). Continue to serve the myosins move Cytoskelettelementen against each other. They therefore assume, for example, functions in cell adhesion, the endo-and exocytosis, cell locomotion by creeping, in general deformation of cells (eg, muscle contraction ), etc. Myosin is a motor protein that occurs only in eukaryotes, here, however, always.
• Prestin: A very fast moving motor protein of the outer hair cells of the inner ear. Immunolocalization shows that Prestin is provided in the lateral plasma membranes of the outer hair cells. This is the area that occurs in the electromotility. Prestin ( molar mass: 80 kDa ) belongs to the family of anion transporters, SLC26. The proteins of this family are structurally well preserved and can convey the electroneutral exchange of chloride and carbonate across the plasma membrane of mammalian cells. Two anions prove to be important for the motility of the outer hair cells. In contrast to the enzymatically -operated motor proteins in the direct conversion Prestin electrical voltages causes a mechanical displacement. In order for a motor to cellular proteins is orders of magnitude faster motility is achieved. In order to have this effect, the protein is directly driven by the sensory elements of the outer hair cells over a short distance.

Relationships

Through structural analyzes showed that myosin and kinesin have a very similar core in the motor domain in which the ATP - binding site is located and the conformational change of the protein takes its beginning. It is therefore suggested that kinesin and myosin have a common evolutionary origin, they constitute a family of proteins.

A functional relationship exists to the G proteins are going through GTP consumption a conformational use this conformational change, however, primarily for signal routing.