Proteins from the kinesin-8 family promote microtubule (MT) depolymerization,
a process thought to be important for the control of microtubule length in
living cells. In addition to this MT shortening activity, kinesin 8s are motors
that show plus-end directed motility on MTs. Here we describe a simple model
that incorporates directional motion and destabilization of the MT plus end by
kinesin 8. Our model quantitatively reproduces the key features of
length-vs-time traces for stabilized MTs in the presence of purified kinesin 8,
including length-dependent depolymerization. Comparison of model predictions
with experiments suggests that kinesin 8 depolymerizes processively, i.e., one
motor can remove multiple tubulin dimers from a stabilized MT. Fluctuations in
MT length as a function of time are related to depolymerization processivity.
We have also determined the parameter regime in which the rate of MT
depolymerization is length dependent: length-dependent depolymerization occurs
only when MTs are sufficiently short; this crossover is sensitive to the bulk
motor concentration.Comment: 34 pages, 11 figure