They found that the dots moved more slowly as the traffic increased, but that they were able to travel farther before becoming detached from the microtubule. They also observed the pausing of the quantum dots, with the number of pauses increasing, but the length of the pauses decreasing, as the concentration of motor proteins is increased. The authors hypothesize that as the concentration of motor proteins increased, several of them became bound to each quantum dot. Much like trucks driving side-by-side down a multilane highway, the motor proteins likely became attached to different protofilaments along the microtubule (microtubules are made of 13 parallel protofilaments arranged into a hollow tube).
As an individual protein encountered an obstacle (another motor protein, for example), the motion of the dot would pause until the force exerted by the other proteins attached to the dot caused it to become detached from the blocked protein. The greater the number of proteins pulling the dot along the microtubule, the greater the force acting on it and the more quickly it would become detached from blocked proteins (and thus, the briefer the pauses in its forward motion).
In this way, motor proteins were able to cooperate to move cargo around roadblocks and to keep cargo attached to the microtubules despite heavy traffic, Tzel says. "This is the first study to really look at the operation of the intracellular transportation system crowded conditions that are typical of living cells," he noted.
"It is important to understand how this system works and what can keep it from functioning properly because it is vital to the survival of all animal cells and motor proteins that make many fundamental biological processes, such as cell division, possible," he adds. "When the transport mechanism fails to work properly, it can lead to a variety of illnesses, including neurodegenerative diseases like Huntington's and
|Contact: Michael Dorsey|
Worcester Polytechnic Institute