Tom Sephton,
It's any protein that uses chemical energy, specifically ATP hydrolysis, to produce physical force.
Proteins that transport molecules and vesicles along the cytoskeleton; enzymes involved in DNA strand separation and replication, such as helicases, gyrases, and topoisomerases; and ATPases that move ions and large organic molecules across membrances are all motor proteins. Their genes have the same sequences to encode their ATP-hydrolyzing motor domains.
There are three superfamilies, comprising myosins, which travel along actin filaments, and kinesins and dyneins, which travel along microtubules. ATP hydrolysis causes a conformational change in these proteins' globular motor domains, allowing them to "walk" along their associated filaments (see Feature, p. 19). These superfamilies contain dozens of individual proteins, and new ones are still being characterized.1
Every cell has its own inventory of motors. In muscle cells, thick filaments of myosin pull on thin actin filaments, causing contractions. In neurons, kinesins use ...
