Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 26, Pages 9844-9849Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0601255103
Keywords
catch bonds; dynamic force spectroscopy; laser trap; myosin
Categories
Funding
- NHLBI NIH HHS [HL 64381] Funding Source: Medline
- NIAMS NIH HHS [AR 45604] Funding Source: Medline
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Muscle contraction and many other cell movements are driven by cyclic interactions between actin filaments and the motor enzyme myosin. Conformational changes in the actin-myosin binding interface occur in concert with the binding of ATP, binding to actin, and loss of hydrolytic by-products, but the effects of these conformational changes on the strength of the actomyosin bond are unknown. The force-dependent kinetics of the actomyosin bond may be particularly important at high loads, where myosin may detach from actin before achieving its full power stroke. Here we show that over a physiological range of rapidly applied loads, actomyosin behaves as a catch bond, characterized by increasing lifetimes with increasing loads up to a maximum at approximate to 6 pN. Surprisingly, we found that the myosin-ADP bond is possessed of longer lifetimes under load than rigor bonds, although the load at which bond lifetime is maximal remains unchanged. We also found that actomyosin bond lifetime is ultimately dependent not only on load, but loading history as well. These data suggest a complex relationship between the rate of actomyosin dissociation and muscle force and shortening velocity. The 6-pN load for maximum bond lifetime is near the force generated by a single myosin molecule during isometric contraction. This raises the possibility that all catch bonds between load-bearing molecules are mechanokinetically tuned to their physiological environment.
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