Motorprotein

Motor proteins are a class of molecules that convert chemical energy from ATP hydrolysis into mechanical work, enabling movement along cytoskeletal filaments. They drive intracellular transport, muscle contraction, and the organization of the mitotic spindle, among other cellular processes.

Each motor binds a filament with a motor domain that catalyzes ATP hydrolysis. The cycle of ATP binding, hydrolysis, Pi release, and ADP release induces conformational changes that produce a mechanical step, the power stroke. Detachment and reattachment allow progression along the filament. Directionality depends on the motor family: kinesins generally move toward microtubule plus ends; cytoplasmic dyneins toward minus ends; most myosins move toward actin filament plus ends.

The three major families are myosin, kinesin, and dynein. Kinesins and dyneins move along microtubules, whereas myosins move along actin filaments. Kinesin-1 is highly processive and performs small, 8-nm steps; dynein is a large, multisubunit motor that requires cofactors such as dynactin for sustained movement; myosin V is a prominent, processive actin motor that transports cargo over long distances.

Roles include transport of vesicles and organelles, positioning of mitochondria, endosomes, and mRNA, and participation in cell division through spindle assembly and chromosome movement. In muscle, myosin II generates contraction by sliding actin filaments, while in cilia and flagella axonemal dyneins drive bending motions.

Structure and regulation: motors typically contain a conserved ATPase motor domain, a lever arm for amplifying motion, and a tail region for cargo binding. Activity is modulated by light chains, adaptor proteins, and post-translational modifications, coordinating motor function with cellular needs.