Structural and cell biology of mitosis and microtubule motors
Microtubules are dynamic polymers made of tubulin dimers that undergo stochastic switching between growth and shrinkage, marked by catastrophe and rescue events. These highly dynamic microtubule polymers rely on microtubule-associated proteins, such as kinetochore proteins and motors to drive the formation of the bipolar spindle, kinetochore-microtubule attachments and chromosome segregation during mitosis. Our goals are to understand how microtubules and their regulatory players mechanistically control the spindle and cell division.
Kinetochores and microtubules
Over the past few years, we have focused on how kinetochore-bound mitotic motors and the outer kinetochore work to drive accurate chromosome segregation. A robust attachment of the kinetochore to the microtubule is essential to segregate the sister chromosomes to the opposite poles. The yeast Dam1 complex is a ten-protein complex found at the outer kinetochore and essential for chromosome segregation. In vitro, the Dam1 complex self-assembles as a ring around microtubules and harnesses the energy produced by depolymerising microtubules to produce force and movement. This makes the Dam1 complex an excellent candidate for coupling microtubule depolymerisation to chromosome movement.
After many years of controversy over how the Dam1 complex binds to microtubules, our srecent work revealed the molecular basis for the interaction between the Dam1 complex and microtubules (Legal et al, 2016). We demonstrated that both the C termini of the Duo1 and Dam1 subunits are necessary and sufficient for this interaction (Figure 1). We also defined the structural arrangement of the Dam1 using crosslinking in collaboration with Juri Rappsilber. Further understanding the architecture of the Dam1 complex is essential to understand how it self-assembles around microtubules in the future.
Mitotic motors and microtubule dynamics
Work in the lab also focuses on kinesin motors, in particular microtubule depolymerases of the kinesin superfamily Kinesin-13. Kinesin-13 motors play an important role in remodeling the microtubule cytoskeleton at mitotic onset to shape the mitotic spindle and align the chromosomes. Kinesin-13 are atypical motors in that they do not translocate along microtubules. Instead they diffuse, which raises the question of how they reach microtubule ends. We showed previously that the Kinesin-13 MCAK undergoes a large conformational change as it binds to microtubules (Talapatra et al, 2015). We are using a multi-disciplinary approach to further understand how Kinesin-13 motors engage with the lattice and reach microtubule ends to achieve efficient microtubule destabilisation.
Legal T., Zou J., Sochaj A., Rappsilber J., Welburn JPI. Molecular architecture of the Dam1 complex-microtubule interaction. (2016).
Open Biology. DOI: 10.1098. PMID: 26962051.
Ye A., Deretic J., Hoel C.M., Hinman AW., Cimini D., Welburn JPI, Maresca TJ. Aurora A kinase contributes to a pole-based error correction pathway. Current Biology (2015).
Talapatra S., Harker B., Welburn JPI. The C-terminal region of MCAK controls its activity and structure through a major conformational switch. Elife (2015). Analysis of microtubule dynamic regulators highlights length-dependent anisotropic scaling of spindle shape. Biology Open. (2014). 3:1217-1223. Young S., Besson S., Welburn JPI.