Visualization of beta-sheets and side-chain clusters in two-dimensional periodic arrays of streptavidin on phospholipid monolayers by electron crystallography

The biotin-binding protein streptavidin was crystallized as two-dimensional periodic arrays on biotinylated phospholipid monolayers, Electron diffraction patterns and images of the arrays embedded in vitreous ice were recorded to near-atomic resolution, Amplitudes and phases of structure factors were computed and combined to produce a 3 Angstrom projection density map. The reliability of the map was verified by comparing it to the available x-ray atomic model of the molecule, Projection densities from p-strands and some amino acid side chains were identified from the electron cryomicroscopy map, These results demonstrate the first near-atomic image of this type of protein periodic array by electron crystallography, which has a great potential to aid in the structural characterization of molecular arrays engineered on a monolayer for various basic or biotechnological applications.