Kinesin-2 from C. reinhardtii Is an Atypically Fast and Auto-inhibited Motor that Is Activated by Heterotrimerization for Intraflagellar Transport

• Published in: Current biology Vol. 30; no. 6; pp. 1160 - 1166.e5
• Main Authors: Sonar, Punam, Youyen, Wiphu, Cleetus, Augustine, Wisanpitayakorn, Pattipong, Mousavi, Sayed I., Stepp, Willi L., Hancock, William O., Tüzel, Erkan, Ökten, Zeynep
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 23-03-2020
• Subjects: auto-inhibition; C. elegans; C. reinhardtii; cilia; flagella; intraflagellar transport; kinesin-2; motor cooperation; flagella; C. elegans; cilia; C. reinhardtii; motor cooperation; kinesin-2; intraflagellar transport; auto-inhibition
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2020.01.046

Construction and function of virtually all cilia require the universally conserved process of intraflagellar transport (IFT) [1, 2]. During the atypically fast IFT in the green alga C. reinhardtii, on average, 10 kinesin-2 motors “line up” in a tight assembly on the trains [3], provoking the question of how these motors coordinate their action to ensure smooth and fast transport along the flagellum without standing in each other’s way. Here, we show that the heterodimeric FLA8/10 kinesin-2 alone is responsible for the atypically fast IFT in C. reinhardtii. Notably, in single-molecule studies, FLA8/10 moved at speeds matching those of in vivo IFT [4] but additionally displayed a slow velocity distribution, indicative of auto-inhibition. Addition of the KAP subunit to generate the heterotrimeric FLA8/10/KAP relieved this inhibition, thus providing a mechanistic rationale for heterotrimerization with the KAP subunit fully activating FLA8/10 for IFT in vivo. Finally, we linked fast FLA8/10 and slow KLP11/20 kinesin-2 from C. reinhardtii and C. elegans through a DNA tether to understand the molecular underpinnings of motor coordination during IFT in vivo. For motor pairs from both species, the co-transport velocities very nearly matched the single-molecule velocities, and both complexes spent roughly 80% of the time with only one of the two motors attached to the microtubule. Thus, irrespective of phylogeny and kinetic properties, kinesin-2 motors work mostly alone without sacrificing efficiency. Our findings thus offer a simple mechanism for how efficient IFT is achieved across diverse organisms despite being carried out by motors with different properties.
•FLA8/10/KAP is necessary and sufficient for the anterograde IFT in C. reinhardtii•Heterotrimerization with KAP fully activates the auto-inhibited FLA8/10 motor•Coupled kinesin-2 motors work mostly independently during co-transport
Sonar et al. explain the mechanism of the atypically fast kinesin-2-driven intraflagellar transport in the unicellular green algae C. reinhardtii and provide a simple model of motor cooperation in distantly related uni- and multicellular organisms, which turn out to be remarkably similar.