Figure 3.
Motor activity and cooperation of kinesin-2 motors. (A) A simplified mechanochemical cycle showing plus end-directed stepping of a truncated heterotrimeric kinesin-2 along a MT track (based on [124]). (B) Coupling of different molecular motors in a combinatorial fashion to the same cargo determines overall transport dynamics. (C) Cooperation of heterotrimeric and homodimeric kinesin-2 motors in C. elegans chemosensory cilia is determined by gradients of kinesin-2 motors. Numbered steps are; (1) A stable IFT-train backbone is loaded into the cilium and transported through the transition zone (TZ) at ~0.5 μm s−1 mainly by kinesin-II. (2) After navigating the TZ, kinesin-II gradually undocks while, at the same time, OSM-3 motors start docking, resulting in a gradually accelerating IFT train reaching ~1.3 μm s−1 at the end of the middle or proximal segment (PS), and ensuring reliable handover of the IFT-trains. (3) In the distal segment (DS), the train is occupied solely by OSM-3 reaching a terminal velocity of ~1.5 μm s−1. (4) Following turnaround and remodeling at the ciliary tip, the backbone is returned to the base by IFT dynein, recycling OSM-3. (5) OSM-3 undocks from retrograde IFT trains along the PS, while kinesin-II gradually docks. (6) Close to the base, kinesin-II is the main kinesin cargo of retrograde IFT trains. Figure based on [78], see text for details.