CYK4 Promotes Antiparallel MicrotubuleBundling by Optimizing MKLP1 NeckConformation
2015
Centralspindlin, a constitutive 2:2 heterotetramer of MKLP1 (a kinesin-6) and the non-motor
subunit CYK4, plays important roles in cytokinesis. It is crucial for the formation of central
spindle microtubule bundle structure. Its accumulation at the central antiparallel overlap
zone is key for recruitment and regulation of downstream cytokinesis factors and for stable
anchoring of the plasma membrane at the midbody. Both MKLP1 and CYK4 are required
for efficient microtubule bundling. However, the mechanism by which CYK4 contributes to
this is unclear. Here we performed structural and functional analyses of centralspindlin
using high-speed atomic force microscopy, Forster resonance energy transfer analysis,
and in vitro reconstitution. Our data reveal that CYK4 binds to a globular mass in the atypically
long MKLP1 neck domain between the catalytic core and the coiled coil and thereby
reconfigures the two motor domains in the MKLP1 dimer to be suitable for antiparallel microtubule
bundling. Our work provides insights into the microtubule bundling during cytokinesis
and into the working mechanisms of the kinesins with non-canonical neck structures.
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