Figure 6.

A model of the CARD/caspase-9 complex. In this model, the building block is the CARD:prodomain heterodimer, which creates a novel surface onto which the catalytic subunit of caspase-9 docks. This docking stabilizes the interactions between two units of the CARD:prodomain heterodimer, which forms a donut-shaped structure. This docking also rearranges the active site of caspase-9 for higher activity. The CARD/caspase-9 complex may resemble the holoenzyme, in which oligomerization is further stabilized by the CED-4 homology domain of Apaf-1.