A Mutational Epitope for Cytochrome c Binding to the Apoptosis Protease Activation Factor-1

Cytochrome c (Cc) binding to apoptosis protease activation factor-1 (Apaf-1) is a critical activation step in the execution phase of apoptosis. Here we report studies that help define the Cc:Apaf-1 binding surface. It is shown that a large number of Cc residues, including residues 7, 25, 39, 62–65, and 72, are involved in the Cc:Apaf-1 interaction. Mutation of residue 72 eliminated Cc activity whereas mutations of residues 7, 25, 39, and 62–65 showed reduced activity in an additive fashion. The implications of this binding model for both recognition and modulation of protein-protein interactions are briefly discussed.