ELECTRON CRYSTALLOGRAPHIC STUDIES OF ACROSOMAL BUNDLE

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Acrosomal bundles from Limulus sperm can be considered as three-dimensional quasi-crystals and reconstructed using a crystallographic approach. However, they are neither "infinitely" large with respect to the borders of the bundle, nor are they a single unit cell in thickness along the viewing direction. Also, because of their shape, bundles do not generally have a preferred azimuthal orientation, which poses challenges for orientation estimation and refinement. We have developed a strategy for recording and processing electron cryo-microscopic images that differs from classical two-dimensional crystalline reconstruction techniques. These developments allowed us to merge data from tomographic tilt series of ice-embedded acrosomal bundles. The goal is to accurately determine amplitudes and phases at the diffraction maxima in terms of hkl indices, and compute a three-dimensional map from the diffraction data. Our research effort in this project has resulted not only in novel structural information about the bundle but also led to an enhancement of our research infrastructure in terms of experimental and computational capabilities.