TY - JOUR T1 - The Orphan Kinesin PAKRP2 Achieves Processive Motility Via Noncanonical Stepping JF - bioRxiv DO - 10.1101/430736 SP - 430736 AU - Allison M. Gicking AU - Pan Wang AU - Chun Liu AU - Keith J. Mickolajczyk AU - Lijun Guo AU - William O. Hancock AU - Weihong Qiu Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/09/29/430736.abstract N2 - 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 exhibits processive plus-end-directed motility on single microtubules as individual homodimers despite having an exceptionally long (32 residues) neck linker. Furthermore, using high-resolution nanoparticle tracking to visualize motor stepping dynamics, we find that PAKRP2 achieves processivity via a noncanonical stepping mechanism that includes small step sizes and frequent lateral steps to adjacent protofilaments. We propose that the small steps sizes are due to a transient intermediate step that involves a prolonged diffusional search of the tethered head due to its long neck linker. Despite this different stepping behavior, ATP is tightly coupled to each 8-nm step. Collectively, this study reveals PAKRP2 as the first orphan kinesin to demonstrate processive motility and broadens our understanding of the diverse kinesin stepping mechanisms. ER -