A synthetic ancestral Kinesin-13 depolymerises microtubules faster than any natural depolymerising kinesin

The activity of a kinesin is largely determined by the ~350 residue motor domain and this region alone is sufficient to classify a kinesin as a member of a particular family. The Kinesin-13 family are a group of microtubule depolymerising kinesins and are vital regulators of microtubule length. Members of this family are critical to spindle assembly and chromosome segregation in both mitotic and meiotic cell division and play crucial roles in cilium length control and neuronal development. To better understand the evolution of microtubule depolymerisation activity in the Kinesin-13 family, we created a synthetic ancestral Kinesin-13 motor domain. This phylogenetically-inferred ancestral motor domain is the sequence predicted to have existed in the common ancestor of the Kinesin-13 family. Here we show that the ancestral Kinesin-13 motor depolymerises stabilised microtubules faster than any previously tested depolymerase. This potent activity is more than an order of magnitude faster than the most highly studied Kinesin-13, MCAK and allows the ancestral Kinesin-13 to depolymerise doubly-stabilised microtubules that are unaffected by MCAK. These data suggest that the ancestor of the Kinesin-13 family was a ‘super depolymeriser’ and that members of the Kinesin-13 family have evolved away from this extreme depolymerising activity to provide more controlled microtubule depolymerisation activity in extant cells. ### Competing Interest Statement The authors have declared no competing interest.