Michael K. Reedy
Professor Emeritus of Cell Biology

Among known muscles, none show greater macromolecular order than certain insect flight muscles (IFM). Our favorite IFM is that of giant Lethocerus waterbugs. Even after permeabilization, glycerination, and months to years of storage at -80°C, its near-crystalline lattices of myofilaments and crossbridges preserve unimpaired mechanical and structural responses in (and transitions between) a multitude of physiological and pharmacological states. With collaboration from five outside labs, we are currently pursuing a 3-way approach to clarify individual motor actions and integrated ensemble performance of myosin crossbridges, by combining X-ray diffraction and quick-freezing for electron microscopy with mechanical (tension) monitoring of muscle fibers in contraction and related states. Synchrotron-source fiber X-ray patterns from exposures lasting 0.1 to 100 msec correlate closely with computed image Fourier transforms of thin-section electron micrographs (EMs) from fibers quick-frozen in 0.1-1 ms. 3-D EM tomography provides density maps of quick-frozen crossbridges into which molecular models of actin and myosin are fitted to discover the pre-force (weakly bound) and active working-stroke conformations and molecular choreography of these interacting molecules. Structural responses to sudden changes in length or temperature are especially informative. High-resolution cryo-X-ray diffraction (to ~7Å) of fibers rapidly and homogeneously frozen, and computer modeling to simulate experimental X-ray patterns round out our approach. Present funding is assured through 2005.
Supporting background research in all six labs seeks to improve all the methodologies involved; the focus in our lab is on bettering cryostorage and cryofixation.

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