(A) A composite map of the active apoptosome reveals density for eight CARDs in the acentric disk shown in top, tilted and side views. Density for the pc-9 CARD in position 8p has been included, although it is present at lower occupancy. Apaf-1/pc-9 CARD pairs that share a Type II interface have been color-coded and Apaf-1 subunits that contribute an ordered CARD to the disk are indicated by color-coded arrow heads. Apaf-1 CARD-NBD linkers are shown in gold and the linker to CARD 7a is marked with a black dot. (B) Close-up views are shown of the CARD disk, viewed in three equi-spaced angular orientations about the center of the apoptosome. The α-helical nature of the CARDs is clearly visible along with the progressive tilt of the pairs as they spiral about the center of the disk. CARD pairs are rendered as surfaces and individual CARD positions are indicated (1a, 3a, 5a and 7a for Apaf-1; 2p, 4p, 6p and 8p for pc-9). Individual linkers are shown as segmented density in gold for the four Apaf-1 CARDs. (C) Similar views to panel B are shown, but as transparent surfaces with docked ribbon CARD models color-coded green for Apaf-1 and purple for pc-9. Only two CARD pairs are shown with ribbons in each panel to highlight their interactions. Some Type I and II interfaces are indicated. CARD-NBD linkers have been omitted for clarity.