Fig. 5: Evaluation of the inter-subunit interfaces for kinesin-2-mediated intraflagellar transport.

a Diagram of sensory cilia (amphid cilia in the head and phasmid cilia in the lateral tail) on neurons of C. elegans (left). Right panel: the cartoon of section through amphid and phasmid cilia showing the longitudinal differentiation of sensory cilia into base, middle segments (m.s.) and distal segments (d.s.). b Rescue experiments of the accelerated IFT phenotype of the kap-1 null allele by wild-type KAP-1 and its mutants. Fluorescence micrographs showing distribution of wild-type and mutant forms of Kap-1::Scarlet along long amphid (upper panels) and phasmid (lower panels) cilia in kap-1(ok676); dyf-11(cas1086) worms. The middle-distal segment junction is indicated by an arrow. Asterisks indicate the ciliary base. Scale bar: 5 μm. Kymographs of intraflagellar transport along the middle segments of cilia are displayed at the far right of each panel. For the kymographs, the horizontal bars represent 5 μm, and the vertical bars represent 5 s. c Quantification of the IFT velocity in the middle segments of cilia. Each experiment is independently repeated three times (n = 3), with the data collected from at least 21 animals (N ≥ 21) in each data set, and the average result is used to represent each experiment. Each bar represents the mean ± SD. n.s. no significant differences, ***p < 0.001, unpaired, two-tailed Student’s t test. Exact p-values are listed in the Source Data file. Source data are provided as a Source Data file. d A schematic model illustrates the assembly of heterotrimeric kinesin-2 for intraflagellar transport. Before association with KAP-1, the motor tails of KLP-11 and KLP-20 remain flexible, while their HTS segments form an intertwined heterodimer to trigger the motor dimerization. This pre-assembled HTS heterodimer specifically captures the C-terminal CTH-hook of KAP-1 to initiate the complex assembly. During this process, the flexible motor tails are co-recognized by KAP-1 and fold together into the central groove of KAP-1, forming the heterotrimeric holoenzyme. Upon the potential phosphorylation of the motor tails, heterotrimeric kinesin-2 could be disassembled to release IFT cargoes and undergo a cycle of assembly and disassembly for intraflagellar transport.