Kinesin

Kinesin and dynein are cellular motor proteins. They serve to transport biological payloads such as proteins, organelles and vesicles along microtubules and drive the movement of flagellar structures and cilia (Hirokawa N et al. 2013). Motor proteins are the molecular motors responsible for the transportation of payloads, often referred to as cargo. The transport mechanism of motor proteins is enabled by the energy harnessed upon cleavage of adenosine triphosophate (ATP). The cyclic hydrolysis of ATP allows the motor protein to repeatedly bind to and unbind from a filament, resulting in stepwise movement. A specific subset of motor proteins, called cytoskeletal motor proteins, move along the filaments of the cytoskeleton. The transport of cargo via cytoskeletal motor proteins is achieved by a mechanochemical cycle consisting of binding to a cytoskeletal filament, a conformational change, release of the filament and relaxation of the conformation. While the mechanochemical step cycles of kinesin and dynein have been studied individually over the last decade, the mechanics of kinesin and dynein and the corresponding measurement methods have not yet been investigated. Therefore, this review focuses on the techniques used to measure the force and velocity capabilities of the cytoskeletal motor proteins kinesin and dynein and the resulting implications (Abraham Z et al. 2018).

The kinesin superfamily (KIF) is made up of fourteen large families (Hirokawa N et al. 2013). To be assigned to the kinesin superfamily, a motor protein must have a specific motor domain. The motor domain specific to KIF molecules is a globular domain that undergoes a consistent ATP- and microtubule-binding sequence to enable locomotion, the transport property that makes KIF molecules motor proteins. The cargoes transported by kinesin bind to the motor domain. In addition, most kinesin families contain two heavy chains, two light chains and an extended coil. As the evolutionary relationships of the individual KIF families become better understood, a new classification nomenclature is now used to distinguish the fourteen major families. This nomenclature is simply Kinesin-1 to Kinesin-14, and although they may have different structures, they are united by their motor domain.

Active transport by kinesin and dynein is a faster and more efficient mode of intracellular transport than diffusion. Moreover, large payloads cannot simply be transferred by diffusion. Therefore, the motor proteins are essential for their translocation. Microtubules provide direct pathways for the movement of motor proteins. Transport can take two forms: anterograde transport and retrograde transport. Anterograde transport, also known as "plus-end", refers to the transport of goods from the center of the cell to the periphery.

Retrograde transport, also known as minus-end transport, refers to the transport of goods from the periphery to the center of the cell (Levy JR et al. 2006). Kinesin motor proteins are inherently restricted to unidirectional locomotion, allowing either anterograde or retrograde transport, with most kinesins performing anterograde transport. The majority of kinesins are responsible for anterograde transport, whereas dynein is more suited to retrograde transport, although dynein motor proteins can also travel in two directions.

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