Cytochrome c (Cyt c), an efficient electron transport protein in cellular respiration that makes biochemical energy ATP, is recently found to take part in initiating apoptosis (programmed cell death) through first oxidizing a lipid called cardiolipin, and then dissociating from the inner membrane of mitochondria to trigger the apoptosis cascade. If cell apoptosis is inhibited, it can cause cancer. Regulation of Cyt c in cardiolipin binding on the mitochondrial membranes potentially enables regulation of the intrinsic pathway of apoptosis. Cardiolipin has four hydrocarbon chains and a negatively charged head group which can interact with anionic site A on Cyt c that contains positively charged lysine amino acids. It is believed that the electrostatic interactions between anionic site A and CL on the inner membrane of a mitochondria lead to protein binding and partial unfolding. In this experiment, we isolate anionic site A, and use cardiolipin liposomes, a spherical sac formed artificially that has a lipid bilayer, to trap Cyt c as a mimic of the concave curvature of the cristae of the mitochondrial inner membrane. Circular dichroism spectroscopy is used to monitor the amount of trapped Cyt c. Previous studies have examined Cyt c-CL binding but using a convex surface that is not physiologically relevant other than it is composed of lipid CL. By comparing to previous similar studies, we can find out whether lipid curvature affects Cyt c-CL binding affinity. The understanding of apoptosis can be used toward novel therapies that can be developed to specifically engage apoptosis in cancer treatments
