  Microtubules are protein polymers that form "molecular highways" for
long-range transport within living cells. Molecular motors actively step along
microtubules to shuttle cellular materials between the nucleus and the cell
periphery; this transport is critical for the survival and health of all
eukaryotic cells. Structural defects in microtubules exist, but whether these
defects impact molecular motor-based transport remains unknown. Here, we report
a new, to our knowledge, approach that allowed us to directly investigate the
impact of such defects. Using a modified optical-trapping method, we examined
the group function of a major molecular motor, conventional kinesin, when
transporting cargos along individual microtubules. We found that microtubule
defects influence kinesin-based transport in vitro. The effects depend on motor
number: cargos driven by a few motors tended to unbind prematurely from the
microtubule, whereas cargos driven by more motors tended to pause. To our
knowledge, our study provides the first direct link between microtubule defects
and kinesin function. The effects uncovered in our study may have physiological
relevance in vivo.
