Michael K. Reedy, MD (University of Washington)
Professor, Department of Cell Biology
Programs: CMB, Structural Biology and Biophysics
458 Sands Bldg., Box 3011
Duke University Medical Center
Durham, NC 27710
We want to know how muscles work by unifying the biochemistry, physiology, and macromolecular structure into one seamless whole. We’re really structure geeks and pursue a real-time, atomic resolution, 3D “movie” that tells us, What does motility look like?
Our two main themes are the motor’s action: myosin hydrolyzing ATP to pull on actin filaments, and the motor’s regulation: tropomyosin and troponin cooperating to either block or allow myosin’s access to actin.
Our lab is unique worldwide because we combine monitoring of the muscle fiber’s physiological (force) response to biochemical and/or length changes with simultaneous monitoring of the molecular structure via either live X-ray fiber diffraction movies, or 3D electron microscopy of fibers instantly cryo-trapped during the experiment.
Our best structural results come from the nearly crystalline flight muscles of the giant waterbug Lethocerus. We are the first and only lab to 3D image myosin and actin working within the native filament array, the sarcomere, which is the basic unit of contraction in all striated muscles. By fitting crystallography-derived models into the electron microscopy structures we are approaching a quasi-atomic understanding of myosin’s motor action.
Stretch an active muscle and it will pull back harder: that’s stretch activation, a response that drives flight in most insects. Our X-ray movies uncovered the molecular mechanism of stretch activation in Lethocerus and now compel us to consider vertebrate muscle. We think we’re poised to uncover the molecular mechanism behind the long known but poorly understood Frank-Starling Law, which describes the heart’s automatic response to squeeze harder if more blood enters the ventricle and stretches the muscle.
Understanding this essential regulation of contraction in response to stretch is a major new research focus for us in the next five years. We also continue our work imaging the structural changes of the myosin motor within the sarcomere during contraction. Funding is currently guaranteed until Fall 2017
Wu S, Liu J, Reedy MC, Perz-Edwards RJ, Tregear RT, Winkler H, Franzini-Armstrong C, Sasaki H, Lucaveche C, Goldman YE, Reedy MK, Taylor KA (2012) Structural changes in isometrically contracting insect flight muscle trapped following a mechanical perturbation. PLoS One. 7(6):e39422
Perz-Dwards RJ, Reedy MK (2011) Electron microscopy and x-ray diffraction evidence for two Z-band structural states. Biophys J. 101(3):709-17
This paper breaks open the long-standing mystery of stretch activation:
Perz-Edwards, R.J., Irving, T.C., Baumann, B.A.J., Gore, D., Hutchinson, D.C., Krzic, U., Porter, R.L., Ward, A.B., & Reedy, M.K. (2011). X-Ray diffraction evidence for myosin-troponin connections and tropomyosin movement during stretch activation of insect flight muscle. PNAS 108(1):120-125.
This paper explores a curious structural change in the Z-band of veretbrate muscle:
Perz-Edwards, R.J. & Reedy, M.K. (2011). Electron microscopy and X-Ray diffraction evidence for two Z-band structural states. Biophysical Journal 101:709-717.
Three-dimensional, quasi-atomic details of myosin's working stroke in real sarcomeres:
Wu, S. Liu, J., Reedy, M.C., Tregear, R.T., Winkler, H., Franzini-Armstrong, C., Sasaki, H., Lucaveche, C., Goldman, Y., Reedy, M.K. & Taylor, K.A. (2010). Electron tomography of cryofixed, isometrically contracting insect flight muscle reveals novel actin-myosin interactions. PLoS One 5(9):e12643.
Modeling of the native myosin head structure from the rich X-ray fiber diffraction pattern:
AL-Khayat, H.A., Hudson, L., Reedy, M.K., Irving, T.C. & Squire, J.M. (2003). Myosin head configuration in relaxed insect flight muscle: X-ray modelled resting crossbridges in a pre-powerstroke state are poised for actin binding. Biophys J 85:1063-1079.
Our first major foray into time-resolved X-ray diffraction of contracting muscle:
Tregear, R.T., Edwards, R.J., Irving, T.C., Poole, K.J.V., Reedy, M.C., Schmitz, H., Towns-Andrews, E. and Reedy, M.K. (1998) X-ray diffraction indicates that active crossbridges bind to actin target zones in insect flight muscle. Biophys.J. 74:1439-1451.
The first ever 3D reconstruction of myosin and actin within the native sarcomere:
Taylor, K.A., Reedy, M.C., Cordova, L., & Reedy, M.K. (1984). Three-dimensional reconstruction of rigor insect flight muscle from tilted thin sections. Nature 310:285-291. -PDF-
Ancient history now, but this classic paper launched the swinging crossbridge theory:
Reedy, M.K., Holmes, K.C., & Tregear, R.T. (1965). Induced changes in orientation of the cross-bridges of glycerinated insect flight muscle. Nature 207:1276-1280. -PDF-