Dr. Jonas Wilson, MD, Ing. Med.
Dynein, one of three cytoskeletal motor protein families, was first identified a half century ago and got its name after the ‘dyne’ (i.e. a unit of force).
Motor proteins are fueled by ATP and are essential for the movement, division and spatial organization of eukaryotic cells, as well as the generation of forces great enough to enable the transport of cellular cargo along what may be called cytoskeletal highways. The importance of these cytoskeletal motor proteins is seen where any dysfunction within them can result in serious disease implications.
Dynein carries out its duties as a protein complex. It is constructed around subunits called heavy chains that are capable of generating forces. These chains are so named due to their hefty molecular masses and motor domains belonging to the AAA+ superfamily, attached to divergent amino-terminal tail domains. These tail domains possess distinct properties with regards to oligomerization and they allow for the binding of a variety of associated subunit types. These subunits in turn are mediators for cargo interaction/ binding, which may occur directly, or may be achieved via adaptor proteins.
Functions of Dynein
Dynein performs a number of cytoplasmic cellular functions. It serves as the power behind the transport of membrane-bound tubules and vesicles in conjunction with their occupant molecules. This cargo is transported towards the minus ends of the microtubule.
Organelles transported along the cytoskeletal highways include lysosomes, endosomes, phagosomes, peroxisomes, melanosomes, mitochondria, lipid droplets and endoplasmic reticulum vesicles that are headed for the Golgi. This transportation can also be employed for the transmission of certain signals across cellular regions. Furthermore, some recent data suggests that dynein may be involved in the translocation of proteins spanning the membrane and lipid-bilayer-signaling complexes.
Dynein is also involved in the clearance of peripheral cellular debris that need to be degraded and/ or recycled. For example, auto-phagosomes engulf proteins and organelles at distal neuronal points and transport these cargo in a dynein-dependent fashion towards the cell body for processing. In addition to these functions, dynein may play a role with certain viruses, albeit involuntary, in the migration to the nucleus of the cell. An example of this would be the resourcefulness of the human immunodeficiency virus (HIV), hijacking dynein to reach its intended nuclear destination.
Additional functions of dynein include its capacity to exert tension on structures within the cell. A force tugging on microtubule networks can be generated and maintained by dynein proteins that are tethered within the cellular cortex. Dynein accomplishes this by one of two ways; either by its migrations towards the microtubule’s minus end or by coupling itself to a plus end of the microtubule that is disassembling. It can thus pull the cytoskeletons of microtubules towards a T cell’s immunological synapse, or it can pull the cytoskeleton of microtubules in migrating fibroblasts and neurons toward the leading edge.