The conformational changes of apocytochrome [formula omitted] upon binding to phospholipid vesicles and micelles of phospholipid based detergents: a circular dichroism study

Abstract

The influence of lipid aggregates on the secondary structure of the mitochondrial precursor protein apocytochrome c was investigated by circular dichroism techniques. A conformational change of the protein from a random coil to partially α-helical structures was observed upon binding to negatively charged DOPS SUVs. Also DOPC SUVs showed to induce such a conformational change, but to a lesser extent. The detergents decyl-, lauryl and myristoyl-phosphoglycol or -phosphocholine, were synthesized as micel forming phospholipid analogs and are shown to mimic the phospholipids well in their ability to induce α-helices in the protein. A full assignment of the regions where the possible α-helices are formed is proposed by making use of derived fragments of apocytochrome c, prediction methods and the known X-ray structure of cytochrome c. Besides a helix at the N-terminus (residues 1–22) and at the C-terminal part (residues 80–101), two regions in the middle section (residues 49–54 und 59–70) are suggested to be helical. It is inferred that the two cysteines in the positions 14 an 17 at the N-terminal part are facing in the same direction, which could facilitate the covalent attachment of the heme group to the precursor in the translocation process.