The Orphan Kinesin PAKRP2 Achieves Processive Motility Via a Noncanonical Stepping Mechanism

PAKRP2 is an orphan kinesin in Arabidopsis thaliana that is thought to transport vesicles along phragmoplast microtubules for cell plate formation. Here, using single-molecule fluorescence microscopy, we show that PAKRP2 is the first orphan kinesin to exhibit processive plus-end-directed motility on single microtubules as individual homodimers. Our results show that PAKRP2 processivity is achieved despite having an exceptionally long (32 residues) neck linker. Furthermore, using high-resolution nanoparticle tracking, we find that PAKRP2 steps via a hand-over-hand mechanism that includes frequent side steps, prolonged diffusional search of the tethered head, and tight coupling of the ATP hydrolysis cycle to the forward stepping cycle.

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