Our laboratory is using 3-D electron microscopy (3DEM) to determine the structures of proteins and macromolecular assemblages in muscle and the cytoskeleton. On e of our projects investigates the structure of myosin crossbridges in different states using the highly ordered filament lattice of insect flight muscle (IFM). In concert with the structural studies, we are developing 3-D reconstruction algorithms uniquely suitable for studying mu scle structure.

We are also developing methods for analyzing the structure of paracrystalline specimens. This research is an outgrowth of our studies on IFM structure, but the technology is applicable to many paracrystalline specimens. One of these techniques is a unique tomographic reconstruction method that uses crosscorrelation methods to align the images in a tilt series. To deal with the specimen disorder, which is manifest as variations in crossbridge structure, we are extending the widely used methods of 2-D correspondence analysis to 3-D mot ifs obtained by tomography. Finally, the knowledge of the atomic structure of the two important proteins in muscle contraction, myosin and actin, provides a uni que opportunity to extend the low-resolution information obtained by 3DEM to atomic resolution.

The first and most important step in electron crystallography is the formation of 2-D crystalline arrays, which are the most suitable specimen for this technique. The first protein that we have successfully crystallized by this method is alpha-actinin. We have also developed technology for ass embly of multiprotein complexes on lipid monolayers as 2-D paracrystalline arrays. These arrays make structural analysis easier because they remove superpositio n problems that complicate image interpretation. The methodology for formation of what we call 2-D bundles open a number of avenues for research into the struct ure of the cytoskeleton.