KIF3

KIF3 refers to a subfamily of kinesin-2 motor proteins that operate as heterotrimeric motors in many animals. In vertebrates, the functional kinesin-2 motor commonly consists of two kinesin–family heavy chains, KIF3A and either KIF3B or KIF3C, together with an accessory subunit known as KAP (kinesin-associated protein, also referred to as KAP3). The canonical form is KIF3A/KIF3B/KAP, while a paralogous variant with KIF3A and KIF3C can also form a motor with KAP. These motors are mainly involved in anterograde transport along microtubules.

Functionally, KIF3-based motors drive intraflagellar transport (IFT) within cilia and flagella, moving IFT trains from the base toward the ciliary tip and facilitating the assembly, maintenance, and signaling functions of cilia. They also participate in cargo transport in other polarized cells, including neurons, where they contribute to the trafficking of signaling receptors, membrane components, and organelles.

Structure and regulation: KIF3A and the partner heavy chain form a heterodimer that associates with KAP, producing a functional motor. Regulation involves autoinhibition relieved by cargo binding and interactions with IFT complex components, enabling ATP-driven movement along microtubules.

Clinical and developmental relevance: Proper KIF3 function is essential for ciliogenesis and ciliary maintenance. Genetic disruption or malfunction of KIF3 components can lead to ciliopathy-related phenotypes in model organisms and contribute to developmental defects due to impaired ciliary signaling.

See also: kinesin-2, KIF3A, KIF3B, KIF3C, KAP3, intraflagellar transport.