The structural dynamics of the kinesin-2 stalk heterodimer and its biological relevance.

Association between two motor subunits through the rod/stalk domain enables molecular motors to walk processively on protein filaments. Previous studies suggested that structural flexibility in the coiled-coil stalk of kinesins is essential for processive runs. The stalk of heterotrimeric kinesin-2, a comparatively less processive motor, is unstable at ambient temperature. How this structural instability impacts the motor function is unclear. Here, using the Förster Resonance Energy Transfer based assays, we show that the Drosophila kinesin-2α/β stalk heterodimer is dynamic at physiological conditions. We further show that insertion of a missense mutation (Glu551-Lys) at the C-terminal half of kinesin-2α stalk reduces the dynamics of the heterodimeric stalk in vitro. The mutation, isolated as a recessive lethal allele in a forward genetic screen, is reported to disrupt the motor function in axonal transport and cilia development. Together these two results suggest that the dynamic instability of the kinesin-2 stalk could play a crucial role in maintaining its biological function.