Background

The kinesin superfamily (KIFs) of motor proteins move along microtubules in an ATP-dependent manner. They perform various functions, and a sub group, known as mitotic kinesins, plays major roles during cell division. Eg5, a microtubule plus end directed kinesin, promotes bipolar spindle formation and elongation and is a validated target in cancer chemotherapy. Recently, it has been shown that Eg5’s role is not exclusive and, under certain conditions, KIF15 can take over this role. We have elucidated the X-ray crystal structure of the KIF15 motor domain, giving insight to both structure and function and this will serve as a platform for future structure-based drug design.

Method

The cDNA for the KIF15 motor domain was cloned into a modified pETM20 vector.  The protein was expressed in E. coli and purified using IMAC and gel filtration chromatography. Crystallisation conditions were identified by nanodrop screening and the structure was determined using molecular replacement.

Results

The structure was solved by molecular replacement and refined to a resolution of 2.8 Å. Crystals showed merohedral twinning which was taken into account during data refinement. KIF15 has been crystallised with three molecules in the asymmetric unit with Mg²⁺ADP bound in the catalytic side. In all three molecules, the helix a4 cluster has moved upwards allowing the neck linker to dock to the motor domain. The crystal structure of KIF15 motor domain gives further insights into the conserved kinesin motor domain.

Conclusion

The crystal structure of the KIF15 motor domain reveals a globular domain, consistent with other kinesin motor domain structures. Currently, efforts are under way to validate Kif15 as a novel potential drug target and to crystallise KIF15 in complex with Kif15-specific inhibitors for structure-based drug design.