Dynein is a molecular motor protein within cells. It plays a role in many processes that support cellular movement and internal organization. Dynein enables cells to perform functions like transporting internal cargo, facilitating cell division, and enabling the movement of entire cells.
Understanding Dynein
Dynein is a large, multi-subunit protein complex. It is built around heavy chains, which generate force. These heavy chains contain motor domains linked to distinct amino-terminal tail domains. These tail domains allow them to associate with various other subunits.
The associated subunits, including intermediate chains, light intermediate chains, and light chains, mediate cargo interaction and binding. Dynein proteins are categorized into two main types: cytoplasmic dynein and axonemal dynein. Cytoplasmic dynein is found in nearly all animal cells, participating in general cellular functions. Axonemal dynein is located in cells possessing cilia and flagella.
How Dynein Powers Movement
Dynein generates force and movement by interacting with microtubules, which act as cellular tracks. It “walks” along these microtubules, moving towards their “minus” end, which is oriented towards the cell’s center. This directed movement is referred to as retrograde transport.
The energy for dynein’s movement comes from adenosine triphosphate (ATP) hydrolysis. When ATP binds to dynein, it causes a conformational change, leading to the protein detaching from the microtubule. After ATP is hydrolyzed into ADP and inorganic phosphate, the motor domain re-engages with a new binding site. This re-binding and subsequent phosphate release induce a “power stroke,” transmitting force and allowing dynein to step along the microtubule.
Essential Cellular Roles
Dynein performs various functions in cells, contributing to their organization. A major role involves intracellular transport, where dynein carries diverse cellular cargo. This includes membrane-bound vesicles, organelles such as mitochondria, lysosomes, and endosomes, and various proteins. This transport occurs along microtubules, moving materials from the cell’s periphery towards its center.
Axonemal dynein is responsible for the beating motion of cilia and flagella. In structures like cilia, found in airways, or flagella, like those on sperm tails, axonemal dynein causes microtubules to slide past each other. This sliding, constrained by linking proteins, results in a bending motion that propels cells or moves fluids across surfaces.
Dynein also participates in cell division, specifically mitosis. It plays a part in processes like centrosome separation, chromosome movements, and the organization and positioning of the mitotic spindle. During this process, dynein helps pull chromosomes apart towards opposite ends of the dividing cell, ensuring each new cell receives a complete set of genetic material.
Dynein and Human Illness
When dynein does not function correctly, it can lead to various health problems. One condition linked to defects in axonemal dynein is Primary Ciliary Dyskinesia (PCD). In PCD, impaired cilia function leads to chronic respiratory infections and male infertility, as airway cilia cannot effectively clear mucus and sperm flagella cannot move properly. Defects can involve the absence of outer dynein arms or both inner and outer dynein arms.
Dynein dysfunction also connects to certain neurological disorders. Neurons rely on proper cargo transport along their long axons, with dynein mediating retrograde transport towards the cell body. Impaired dynein function can disrupt the delivery of essential materials or waste removal. This contributes to neurodegenerative disorders like Parkinson’s-like Perry Syndrome, or neurodevelopmental diseases including lissencephaly and certain forms of intellectual disability. Additionally, mutations in dynein-encoding genes have been implicated in Charcot-Marie-Tooth disease type 2O, a disorder affecting peripheral motor and sensory neurons.