Kinesin2

Kinesin-2 refers to a family of microtubule-based motor proteins that drive cargo transport toward the plus ends of microtubules, primarily within cilia and flagella. The family includes two main forms: heterotrimeric kinesin-2, consisting of two distinct motor subunits and a non-motor adaptor, and homodimeric kinesin-2, represented by motor proteins that function as dimers without a separate adaptor subunit. In vertebrates, the classic heterotrimeric form comprises two motor subunits, KIF3A and KIF3B, together with a kinesin-associated protein (KAP) that helps link the motor to cargo, including intraflagellar transport particles.

A second, evolutionarily related form is homodimeric kinesin-2, such as KIF17 in vertebrates and OSM-3 in Caenorhabditis elegans, which can function as a motor in cilia and other cellular contexts. These motors share structural features typical of kinesins—dimeric heavy chains with ATPase motor domains, a coiled-coil stalk, and tail regions that interact with cargo—yet differ in subunit composition and cargo adaptors. Kinesin-2 motors are distinguished by their role as primary drivers of anterograde intraflagellar transport (IFT), moving IFT particles and associated cargo from the ciliary base toward the tip. This transport is essential for ciliary assembly, maintenance, and signaling. Retrograde transport from tip to base is carried out by dynein-2, a separate motor system.

Regulation of kinesin-2 activity involves subunit assembly, post-translational modifications, and cargo adaptor interactions that modulate processivity and targeting to cilia. In many organisms, proper function of kinesin-2 is critical for ciliogenesis and sensory cell function. Mutations in kinesin-2 subunits or their adaptors can disrupt ciliary formation and signaling, contributing to ciliopathies in humans and affecting development and physiology in model organisms.