Motor proteins

Motor proteins are class of molecular motors that are able to move along the surface of a suitable substrate. They convert chemical energy into mechanical work by the hydrolysis of ATP. Flagellar rotation, however, is powered by proton pump.

The best prominent example of a motor protein is the muscle protein myosin which "motors" the contraction of muscle fibers in animals. Motor proteins are the driving force behind most active transport of proteins and vesicles in the cytoplasm. Kinesins and cytoplasmic dyneins play essential roles in intracellular transport such as axonal transport and in the formation of the spindle apparatus and the separation of the chromosomes during mitosis and meiosis. Axonemal dynein, found in cilia and flagella, is crucial to cell motility, for example in spermatozoa, and fluid transport, for example in trachea.

The importance of motor proteins in cells becomes evident when they fail to fulfill their function. For example, kinesin deficiencies have been identified as cause for Charcot-Marie-Tooth disease and some kidney diseases. Dynein deficiencies can lead to chronic infections of the respiratory tract as cilia fail to function without dynein. Numerous myosin deficiencies are related to disease states and genetic syndromes. Because myosin II are essential for muscle contraction,defects in muscular myosin predictably cause myopathies. Because myosin are necessary for the process of hearing through their contribution to thestructure of to stereocillia, defects in unconventional myosin can lead to Usher syndrome and non-syndromic deafness.

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