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Vol. 19, Issue 8, 3234-3242, August 2008

This Article Full Text Full Text (PDF) Supplemental Materials All Versions of this Article: E08-02-0206v1 19/8/3234    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Google Scholar Articles by Jung, H. S. Articles by Craig, R. PubMed PubMed Citation Articles by Jung, H. S. Articles by Craig, R.

Head–Head and Head–Tail Interaction: A General Mechanism for Switching Off Myosin II Activity in Cells

Hyun Suk Jung^*, Satoshi Komatsu, Mitsuo Ikebe, and Roger Craig^*

*Department of Cell Biology and Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655

Submitted February 26, 2008; Revised April 14, 2008; Accepted May 8, 2008
Monitoring Editor: Thomas D. Pollard

Intramolecular interaction between myosin heads, blocking key sites involved in actin-binding and ATPase activity, appears to be a critical mechanism for switching off vertebrate smooth-muscle myosin molecules, leading to relaxation. We have tested the hypothesis that this interaction is a general mechanism for switching off myosin II–based motile activity in both muscle and nonmuscle cells. Electron microscopic images of negatively stained myosin II molecules were analyzed by single particle image processing. Molecules from invertebrate striated muscles with phosphorylation-dependent regulation showed head–head interactions in the off-state similar to those in vertebrate smooth muscle. A similar structure was observed in nonmuscle myosin II (also phosphorylation-regulated). Surprisingly, myosins from vertebrate skeletal and cardiac muscle, which are not intrinsically regulated, undergo similar head–head interactions in relaxing conditions. In all of these myosins, we also observe conserved interactions between the ‘blocked’ myosin head and the myosin tail, which may contribute to the switched-off state. These results suggest that intramolecular head–head and head-tail interactions are a general mechanism both for inducing muscle relaxation and for switching off myosin II–based motile activity in nonmuscle cells. These interactions are broken when myosin is activated.

Address correspondence to: Roger Craig (roger.craig{at}umassmed.edu)

Abbreviations used: ELC, essential light chain; RLC, regulatory light chain; HMM, heavy meromyosin; S2, subfragment 2 of myosin.

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