Molecular Motors in a Nutshell
Central players in intracellular transport processes of eukaryotes are the molecular motors myosin, kinesin and dynein. These molecular machines convert the chemical energy of ATP into mechanical work to move unidirectionally along the cytoskeletal filaments actin and microtubules. At the same time they transport a tremendous variety of cargoes, ranging from large membrane-bound organelles to building blocks for macromolecular complexes and small proteins involved in signaling processes.
To power intracellular long-range transport efficiently, many molecular motors can translocate over long distances without dissociating from their track, a property termed processivity. Just like a tightrope walker, these motors literally walk along their respective filaments, taking discrete steps in a hand-over-hand fashion. Generally, these motors - myosins and kinesin alike - share a similar overall structure and domain organization: Two catalytic subunits form a parallel homodimer with two globular motor domains, containing ATP- and microtubule binding sites that are connected via an elongated coiled-coil stalk domain, followed by the cargo-binding tail domain. Instead of being composed of two identical polypeptide chains like kinesin-1, most kinesin-2 motors form by heterodimerization of two distinct catalytic subunits. This extraordinary structure offers the unique opportunity to extend current models of processivity and regulation.