Kinesin and Dynein-Dynactin at Intersecting
Microtubules: Motor Density Affects Dynein Function.
Biophys J. 94:3115-3125. 2008.
Kinesin and cytoplasmic dynein are
microtubule-based motor proteins that actively transport material
throughout the cell. Microtubules can intersect at a variety
of angles both near the nucleus and at the cell periphery,
and the behavior of molecular motors at these intersections
has implications for long-range transport efficiency and accuracy.
To test motor function at microtubule intersections, crossovers
were arranged in vitro using flow to orient successive layers
of filaments. Single kinesin and cytoplasmic dynein-dynactin
molecules fused with green-fluorescent protein, and artificial
bead cargos decorated with multiple motors, were observed
while they encountered intersections. Single kinesins tend
to cross intersecting microtubules, whereas single dynein-dynactins
have a more varied response. For bead cargos, kinesin motion
is independent of motor number. Dynein beads with high motor
numbers pause, but their actions become more varied as the
motor number decreases. These results suggest that regulating
the number of active dynein molecules could change a motile
cargo into one that is anchored at an intersection, consistent
with dynein's proposed transport and tethering functions in