Dimerization of mammalian kinesin-3 motors results in superprocessive motion

Abstract

The kinesin-3 family is one of the largest among the kinesin superfamily and its members play important roles in a wide range of cellular transport activities, yet the molecular mechanisms of kinesin-3 regulation and cargo transport are largely unknown. We performed a comprehensive analysis of mammalian kinesin-3 motors from three different subfamilies (KIF1, KIF13, and KIF16). Using Forster resonance energy transfer microscopy in live cells, we show for the first time to our knowledge that KIF16B motors undergo cargo-mediated dimerization. The molecular mechanisms that regulate the monomer-to-dimer transition center around the neck coil (NC) segment and its ability to undergo intramolecular interactions in the monomer state versus intermolecular interactions in the dimer state. Regulation of NC dimerization is unique to the kinesin-3 family and in the case of KIF13A and KIF13B requires the release of a proline-induced kink between the NC and subsequent coiled-coil 1 segments. We show that dimerization of kinesin-3 motors results in superprocessive motion, with average run lengths of ∼10 μm, and that this property is intrinsic to the dimeric kinesin-3 motor domain. This finding opens up studies on the mechanistic basis of motor processivity. Such high processivity has not been observed for any other motor protein and suggests that kinesin-3 motors are evolutionarily adapted to serve as the marathon runners of the cellular world.microtubule | molecular motor | helical plot | intracellular transport

Intracellular cargo transport by kinesin-3 motors

“…In contrast, KIF16B is a monomer in the cytoplasm and dimerizes at the cargo surface. The localized dimerization of KIF16B on early endosomes has been directly observed using Fцrster resonance energy transfer (FRET) in live cells [58]. Thus, these examples support the idea that due to the diverse cargo binding tail, the different kinesin 3 fam ily members use diverse means of autoinhibition and cargo dependent release of inhibition, involving changes in the dimerization status for some members and compet itive binding of a peptide region that weakly interacts with the motor domain for others.…”

“…In KIF1A, KIF13A, and KIF13B, the coiled coil domains seem to interfere with dimerization. It has been shown that instead, the neck coil alone efficiently dimerizes these motors [57,58].…”

“…In MmKIF1A, a similar switch through intra and intermol ecular coiled coil formation is proposed to occur between the neck coil region and the first coiled coil domain (CC1). Surprisingly, the truncation of the entire tail results in processive dimeric motors of KIF1A, KIF13A, and KIF13B, while all longer constructs containing CC1 result in monomers that only show diffusive movement [57,58]. If autoinhibition is prevented by deletion of the flexible hinge between the neck helices in C. elegans Unc 104, the motility of the motor in vitro is unperturbed, but transgenic worms show severe defects in the coordination of their movement [73].…”

“…In the KIF13 subfamily, a proline residue at the junc tion of neck coil and CC1 provides the flexibility to enable CC1 to fold back and interact with the neck coil. Deletion of this proline residue results in dimerization via the neck coil domains and active, processive motors [58,84]. Control of the autoinhibited state of the KIF1A motor might also involve the FHA domain and the fol lowing coiled coil CC2.…”

The Arabidopsis kinesin-4, FRA1, requires a high level of processive motility to function correctly

“…Another shared feature of transport kinesins is their ability to move processively (i.e. take many steps upon binding to a microtubule), which enables efficient long-distance transport by single motors (Howard et al, 1989;Soppina et al, 2014;Yamazaki et al, 1995). Consistent with a transport function, dimeric FRA1 motors have been found to move processively both in vitro and in vivo (Kong et al, 2015;Zhu and Dixit, 2011;Zhu et al, 2015).…”