STRUCTURAL BIOLOGY--IMAGE PROCESSING OF ELECTRON MICROGRAPHS

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This project uses image processing techniques to analyze electron micrographs. In order to answer important questions in structural biology, it is necessary to obtain relatively high resolution two- and three- dimensional structural information about biological macromolecules. While atomic or near atomic resolution information has traditionally been available by x-ray crystallography for some small molecules and small proteins, the overwhelming majority of biological macromolecules are not crystalline, or are too large and therefore not amenable to 3-D crystallography. Biological specimens can, on the other hand, be visualized in the electron microscope using a number of specimen preparation techniques. Negative staining and shadowing, which both use heavy metals, are two traditional approaches to increasing contrast to show the biological macromolecule's structure. Cryo-electron microscopy, a newer technique, attempts to preserve "native" structure by surrounding the specimen with a layer of ice. Collaborative studies with LSBR, NIAMS are currently underway on a number of such projects, whereby the electron micrograph images are computationally corrected, combined, averaged, reconstructed, or in some way computationally enhanced to improve the signal-to-noise ratio or to increase the interpretability of the structures being visualized. Cryo images are typically lower contrast and require greater computer processing to achieve satisfactory results. Of particular interest to our research is the understanding of viral structures. At present we are continuing our efforts to investigate the structure of a large animal virus, human herpes simplex virus (type 1). We are in the process of determining the location of the major capsid proteins. Using the three-dimensional icosahedral reconstruction technique, we apply the symmetry of these virus particles both to find the orientation of randomly oriented capsid particles (in ice) and to combine many particles into a three-dimensional reconstruction. Biological material for these herpes reconstructions is provided through collaboration with researchers at the University of Virginia, Charlottesville. The electron microscopy is performed in LSBR, NIAMS. Interpretation of our 3-D reconstructions is performed jointly by all collaborators.