A paper just published in Nature Communications by the Single-Molecule Biophysics Laboratory of Assistant Professor Weihong Qiu reports an unexpected mechanical property of a “motor” protein that offers new insights into how motor proteins help build and maintain the mitotic spindle, the American football-shaped macromolecular structures that animal and fungi cells depend on to ensure accurate chromosome segregation during cell division. Located inside cells, motor proteins are tiny molecular machines that convert chemical energy into mechanical work. They interact with train-track-like structures called microtubules to transport cargos or exert forces.

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The motor protein KlpA moves in one direction on a single microtubule track and switches to the opposite direction between a pair of microtubules. Illustration credit: Kuo-Fu Tseng, Oregon State University.
[click on image to see the motion] The motor protein KlpA moves in one direction on a single microtubule track and switches to the opposite direction between a pair of microtubules. Illustration credit: Kuo-Fu Tseng, Oregon State University.
In this study, Qiu and colleagues focused on a particular motor protein called KlpA, and used a high-sensitivity microscopy method to directly visualize the motion of individual KlpA molecules on microtubules. The Qiu team shows that, while all other KlpA-like motor proteins are believed to move in only one direction on the microtubule track, KlpA has a “reverse” gear that allows it to go in different directions. This enables KlpA to behave differently in when it is operating at different locations within the mitotic spindle. This research may open the door to understand the similar KlpA-like motor proteins in mammals that are implicated in cancer cell proliferation. Understanding the design principle underlying the bidirectional motion of KlpA may also guide the engineering of motor protein-based molecular devices for targeting drug delivery in a controllable manner.

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