Near-complete backbone resonance assignments of acid-denatured human cytochrome c in dimethylsulfoxide: a prelude to studying interactions with phospholipids

Human cytochrome c plays a central role in the mitochondrial electron transfer chain and in the intrinsic apoptosis pathway. Through the interaction with the phospholipid cardiolipin, cytochrome c triggers release of pro-apoptotic factors, including itself, from the mitochondrion into the cytosol of cells undergoing apoptosis. The cytochrome c/cardiolipin complex has been extensively studied through various spectroscopies, most recently with high-field solution and solid-state NMR spectroscopies, but there is no agreement between the various studies on key structural features of cytochrome c in its complex with cardiolipin. In the present study, we report backbone 1H, 13C, 15N resonance assignments of acid-denatured human cytochrome c in the aprotic solvent dimethylsulfoxide. These have led to the assignment of a reference 2D 1H-15N HSQC spectrum in which out of the 99 non-proline residues 87% of the backbone amides are assigned. These assignments are being used in an interrupted H/D exchange strategy to map the binding site of cardiolipin on human cytochrome c.