Dynein

Dynein is a family of large motor proteins that move along microtubules toward their minus end, which is usually near the cell center. Using the energy of ATP, dyneins carry cargo, position the machinery of cell division and power the beating of cilia and flagella.

Cytoplasmic dynein-1 is a large complex of about 1.5 million daltons made of two heavy chains and several smaller subunits, and it works with the partner complex dynactin and adaptor proteins that link it to cargo. Axonemal dyneins are arranged in rows along the doublets of microtubules inside cilia and flagella. The motor domain of the heavy chain is a ring of six units, the site where ATP is broken down and where the movement originates.

Dynein carries vesicles, organelles, mRNA and viruses along the cytoskeleton toward the cell center, including retrograde transport from the end of a nerve axon back to the cell body. It positions the Golgi apparatus and helps shape the spindle that pulls chromosomes apart in mitosis. It works in opposition to kinesin, the motor that usually travels toward the plus end, and both interact with actin and other cytoskeletal parts.

Axonemal dyneins slide neighboring microtubule doublets past one another, which bends the cilium or flagellum, and this is how a sperm swims and airway cilia clear mucus. Mutations in their genes cause primary ciliary dyskinesia, with chronic lung infection and, in some patients, reversed placement of organs in the body. Defects in cytoplasmic dynein are linked to neurodegenerative and developmental disorders, and some viruses hijack it to travel to the nucleus of an infected cell.

• Cytoskeleton — the tracks it travels on
• Mitosis — a process that depends on it
• Actin — another cytoskeletal protein