Mimicking the Mitochondrion: Cytochrome c-Fatty Acyl-CoA Interactions

Abstract

Cytochrome c (cyt c)-cardiolipin (CL) interactions in the mitochondria are required for intrinsic apoptotic signaling in cells.\(^{1-5}\) Recent studies have found that many diseased cells, such as cancer cells, contain abnormal CL content,\(^{6-9}\) which may lead to irregular apoptotic trends. Studies investigating cyt c-CL interactions often use CL or lipid liposomes, which can result in unreliable data,\(^{10, 11}\) making structural studies of the complex difficult. Finding a water soluble, lipid-like molecule that can mimic CL in cyt c-CL interactions would enable more accurate structural studies of the cyt c-lipid complex and would allow for studies investigating cyt c’s interactions with lipids of distinct acyl chains. The present work describes UV-Vis binding experiments, circular dichroism experiments, and peroxidase assays performed to investigate cyt c-fatty acyl- CoA binding. The results revealed that fatty acyl-CoA molecules are good CL mimics because they bind similarly to and induce similar conformational and peroxidase activity changes upon cyt c. Additionally, it was found that fatty acyl-CoAs with longer, unsaturated acyl chains more effectively bind to cyt c while longer, saturated acyl chains more effectively increase cyt c’s peroxidase activity. These conclusions are consistent with past findings that cells containing CL species with shorter acyl chains are less likely to experience mitochondrial cyt c release,\(^{12}\) which is linked to apoptosis.\(^{2,3}\)The reduced conformational changes and peroxidase activity of cyt c upon binding to shorter acyl chains suggests that in vivo, less cyt c-CL binding and CL oxidation, necessary steps to inducing the intrinsic apoptotic pathway,\(^{1,4,5}\) would occur in cells containing CL species with shorter acyl chains (such as cancer cells\(^{6}\)).