The movement of molecular motors that carry a cell's cargo may be controlled in a different manner than previously suspected, according to a paper in this week's Science. The molecular motor kinesin, which carries vesicles, organelles, and other loads along cellular microtubule networks, may not need the networks themselves to move -- a finding that "throws a surprising wrench into existing models of kinesin movement," according to an accompanying commentary by David Hackney of Carnegie Mellon University in Pittsburgh.Kinesin consists of two components, called "heads," that walk in a hand-over-hand fashion along microtubules. Kinesin powers this movement by hydrolyzing adenosine triphosphate (ATP), consuming one molecule per step. Between steps, the motor pauses, and is stalled until ATP binds to a kinesin head. But the exact mechanism for how this ATP "gating" occurs has been controversial. Researchers have proposed two general mechanisms for the ATP gate. In the first...

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