The Kinesin-12 Kif15 is a processive track-switching tetramer

Abstract

Kinesin-12 motors are a little studied branch of the kinesin superfamily with the human protein (Kif15) implicated in spindle mechanics and chromosome movement. In this study, we reconstitute full-length hKif15 and its microtubule-targeting factor hTpx2 in vitro to gain insight into the motors mode of operation. We reveal that hKif15 is a plus-end-directed processive homotetramer that can step against loads of up to 3.5 pN. We further show that hKif15 is the first kinesin that effectively switches microtubule tracks at intersections, enabling it to navigate microtubule networks, such as the spindle. hKif15 tetramers are also capable of cross-linking microtubules, but unexpectedly, this does not depend on hTpx2. Instead, we find that hTpx2 inhibits hKif15 stepping when microtubule-bound. Our data reveal that hKif15 is a second tetrameric spindle motor in addition to the kinesin-5 Eg5 and provides insight into the mechanisms by which hKif15 and its inhibitor hTpx2 modulate spindle microtubule architecture.DOI: http://dx.doi.org/10.7554/eLife.01724.001

Kinesin-12 motors cooperate to suppress microtubule catastrophes and drive the formation of parallel microtubule bundles

“…We previously reported that single hKif15-eGFP homotetramers moving on stabilized microtubules dwell for extended periods of time at the microtubule plus-end (12). This observation prompted us to investigate whether such behavior also occurs on dynamic microtubules and whether it influences their plus-end dynamics.…”

“…These motors are highly processive, capable of switching tracks at microtubule intersections, and can step against loads of up to 3.5 pN (12). Kif15 tetramers can also mediate the cross-linking of two microtubules, but give rise to very little microtubule sliding, except for episodes of short duration transport of short microtubules (12). A second study recently reported that a dimeric Kif15 missing the carboxyl-terminal half of the protein is also able to drive microtubule transport (13).…”

“…As a first step, we recently provided an initial biochemical characterization of full-length human Kif15 motors in vitro (12). We found that at physiological ionic strength hKif15 motors exist as tetramers.…”

“…mitotic spindle, important features of hKif15 activity might be missed by in vitro approaches using stabilized microtubules. For example, the long plus-end dwell time of hKif15 motors suggests that the motor may interfere with microtubule dynamics (12). We therefore aimed to study the behavior of hKif15 motors in networks of dynamic microtubules in vitro.…”

“…We found that at physiological ionic strength hKif15 motors exist as tetramers. These motors are highly processive, capable of switching tracks at microtubule intersections, and can step against loads of up to 3.5 pN (12). Kif15 tetramers can also mediate the cross-linking of two microtubules, but give rise to very little microtubule sliding, except for episodes of short duration transport of short microtubules (12).…”