What type of study is this?

This is a In Vitro Study study.

What question did this study set out to answer?

This research examines the evolution and functional specialization of heterotrimeric kinesin-2 for ciliogenesis.

February 21, 2026

BPS2026 – An evolutionary snapshot of becoming a heterotrimeric kinesin-2 for ciliogenesis

Key Points

This research examines the evolution and functional specialization of heterotrimeric kinesin-2 for ciliogenesis.
Conducted phylogenetic analyses to understand kinesin-2 evolution.
Utilized optical tweezers assay to study structural features promoting dimerization.
Analyzed binding energy shifts between homodimeric and heterodimeric forms.
Identified KIN3 as a crucial component for ciliogenesis that interacts with KAP.
Demonstrated that KIN3 can function as a homodimeric motor and form heterodimers with KIN1 or KIN2.
Found that incorporating kinesin-2-specific folds significantly increases KAP binding strength.

Abstract

Long-range transport within cilia relies on heterotrimeric kinesin-2, composed of a heterodimeric motor and the KAP adaptor. Phylogenetic analyses suggest that heterodimeric kinesin-2 motors evolved independently from homodimers across multiple lineages via gene duplication, yet all converged on KAP binding, indicating strong evolutionary pressure toward heterotrimerization. In Tetrahymena thermophila , a recent duplication event produced KIN1 and KIN2. We found that both are unable to bind KAP. Instead, KIN3, a previously uncharacterized kinesin-2, interacts with KAP. We see that in vivo, KIN1/2 combination cannot compensate for KIN3 loss, nor can KIN3 substitute for KIN1/2, suggesting that KIN3 must heterodimerize with KIN1 or KIN2 to support ciliogenesis. Surprisingly, in vitro, KIN3 functions as a homodimeric processive motor just as well as a KIN3/1 or KIN3/2 heterodimer. Tetrahymena thus offers a unique evolutionary snapshot of a functional homodimeric kinesin-2 acquiring KAP binding and transitioning into a heterotrimeric motor to function in ciliogenesis. Using a single-molecule optical tweezers assay, we identified three structural features that favor heterodimerization: two force-stable coiled-coil segments that promote dimer formation, with homodimeric and chimeric constructs showing 5-fold lower binding energy; and a conserved kinesin-2-specific-fold that enhances KAP affinity. Incorporating this fold into chimeric constructs increased KAP binding 4-fold compared to homodimers. Once KAP is bound, the resulting trimer exhibits a 2-fold increase in force stability. Notably, KAP dissociation kinetics and pathways remain consistent across all constructs, governed primarily by the C-terminal segment of KIN3, with minor contributions from KIN1. We collectively provide the most detailed mechanism of the structural and functional advantages of heterotrimeric kinesin-2 evolution and provide mechanistic insight into its specialization for ciliary transport.

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