Fig. 8

Structure of SlpX and the Ca²⁺-binding site. Crystal structure (a) of domain I (amino acids 31–182) of S-layer protein SlpX from L. acidophilus (PDB 7QFI). The Ca²⁺ ion is shown as a green sphere and the coordinating side chains and main chain atoms are shown as sticks. Detailed close-up view (b) of the Ca²⁺-binding site from (a). The bond distances from each side chain or main chain ligand are labelled in black. Ca²⁺ is shown as a small sphere for a clearer view of the coordination site. A nearby water molecule is shown as a small red sphere.