Fig. 3: Planar crystal packing in the X-ray structure fits the in situ packing of the native S-layer.
a 2D schematic of H/L complex crystal packing, indicating the interaction network linking a single H/L (slate blue/gold) complex with six other molecules in a planar arrangement generated by SLPH tiling. Array is depicted as seen from the extracellular environment, with symbols representing key interaction types in the crystal lattice, detailed in Supplementary Fig. 4. b Cartoon representation of the H/L planar array (PDB ID 7ACY, coloured as in a, views as defined in Fig. 1b). c Native C. difficile S-layer ghosts (electron micrograph, negatively stained, left. Scale bar: 2 µm) were used to compute Fourier transforms (middle). Micrograph is a lower magnification (×3000) of ghosts used to collect the images used (82351x) for Fourier transform computation and is representative of the morphology of S-layer ghosts. Typically spots from two or more lattices were observed. Fourier transform is representative of 36 images collected for R20291. Reciprocal lattice axes (red and white axes) are indicated for two observed lattices (scale bar 0.0125 Å−1). Intact frozen-hydrated C. difficile cells, examined by cryo-electron microscopy (right), show distinctive ridged surface indicated by red arrows (scale bar 50 nm). Micrograph is representative of whole-cell images, which were not used for data analysis and 2D map calculations. Instead, these were computed from homogenised fragments, as described in the Methods section. d, Orthogonal views of the 3D reconstruction of negatively stained S-layer ghost indicating the overall envelope in the native lattice. A rigid body fit of the structure of H/L complex determined by X-ray crystallography (PDB ID: 7ACY, cartoon representation, SLPL - gold, SLPH - slate) indicates a similar arrangement in the native S-layer ghosts and crystal packing. Reconstruction is shown from the environment (top left) and cell wall (top right), and side views in the 2D plane (bottom panels).
