One question Diehl and lead co-authors Kenneth Jamison and Jonathan Driver helped answer in the new study is how much pulling power a pair of kinesins could apply to a cargo compared with the amount applied by a single kinesin.
The apparatus they created to study the problem was years in the making. Driver and Jamison, both graduate students, used strands of DNA to make a scaffold, a sort of molecular yoke that they could use to hitch a pair of kinesins to an experimental cargo. The cargo in their tests was a microscopic plastic bead. Using laser beams in an instrument called an optical trap, they attached teams of bead-pulling proteins to microtubule roadways.
As the motors walked down the road, they pulled the bead away from the center of the optical trap. At the same time, the lasers in the trap exerted counterpressure in an effort to move the bead back to the center of the trap. Eventually, the light won out, forcing the motors to let go and the cargo to snap back to the middle of the beam. By measuring the precise movements of the bead during this reaction, Diehl's team was able to determine exactly how much force a team of motors exerted on a bead.
"Compared with other motors, kinesin is actually a pretty strong performer," he said. "Single kinesin motor molecules can produce relatively large forces, and they rarely step in the wrong direction when walking along microtubules. This is remarkable behavior, considering kinesin is a molecular-scale machine that experiences significant thermal and chemical fluctuations."
Given how well they perform alone, it would be easy to assume that a group of kinesins would pull harder than a single kinesin. But Diehl points out that a team of kinesins can only harness the combined potential of both motors under certain circumstances.
|Contact: Jade Boyd|