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Science 321 (5885): 133-136

Copyright © 2008 by the American Association for the Advancement of Science

Myosin I Can Act As a Molecular Force Sensor

Joseph M. Laakso, John H. Lewis, Henry Shuman, E. Michael Ostap*

Abstract: The ability to sense molecular tension is crucial for a wide array of cellular processes, including the detection of auditory stimuli, control of cell shape, and internalization and transport of membranes. We show that myosin I, a motor protein that has been implicated in powering key steps in these processes, dramatically alters its motile properties in response to tension. We measured the displacement generated by single myosin I molecules, and we determined the actin-attachment kinetics with varying tensions using an optical trap. The rate of myosin I detachment from actin decreases >75-fold under tension of 2 piconewtons or less, resulting in myosin I transitioning from a low (<0.2) to a high (>0.9) duty-ratio motor. This impressive tension sensitivity supports a role for myosin I as a molecular force sensor.

The Pennsylvania Muscle Institute and Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.

* To whom correspondence should be addressed at the Department of Physiology, University of Pennsylvania School of Medicine, B400 Richards Building, Philadelphia, PA 19104–6085, USA. E-mail: ostap{at}

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