STRUCTURAL BIOLOGY--IMAGE PROCESSING OF ELECTRON MICROGRAPHS

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This project uses image processing techniques to analyze electron micrographs. To answer important questions in structural biology, it is necessary to obtain relatively high resolution 2- and 3-D structural information about biological macromolecules. Biological specimens can 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 macromolecules structure. Cryoelectron microscopy, a newer technique, attempts to preserve "native" structure by surrounding the specimen with a layer of ice. Collaborative studies with LSB, NIAMS are currently underway on a number of 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 completing the localization of the major capsid proteins. Using the 3D icosahedral reconstruction technique, we apply the symmetry of these virus particles to both find the orientation of randomly oriented capsid particles (in ice) and to combine many particles into a 3D reconstruction. Biological material for these herpes virus reconstruction is provided through a collaboration with researchers at the University of Virginia, Charlottesville. The electron microscopy is performed in LSB, NIAMS. Interpretation of our 3D reconstructions is performed jointly by all collaborators.