Fig. 2.
Crystal structure of LlPC in complex with c-di-AMP. (A) Schematic drawing of the structure of LlPC tetramer in complex with c-di-AMP. Monomer 1 is colored as in Fig. 1A; monomer 2, in magenta; monomer 3, in cyan; and monomer 4, in yellow. c-di-AMP is shown as a sphere drawing (in black for carbon atoms, labeled cdA). (B) Omit Fo–Fc electron density at 2.3-Å resolution for the PT–BCCP linker in LlPC, contoured at 3σ. (C) Close-up showing the connection between PT and BCCP domains in the LlPC tetramer in complex with c-di-AMP. (D) Schematic drawing for an alternative model for PC catalysis where BCCP visits the BC active site of the other monomer in the same layer of the tetramer, and then visits the CT active site of its own monomer for catalysis. The BC and CT active sites are indicated with the asterisks, and the arrows indicate BCCP translocation during catalysis. (E) A previously proposed model for PC catalysis (28, 31), where BCCP visits the BC active site of its own monomer and then the CT active site of the other monomer.