Importance of phosphatidylethanolamine for the interaction of apocytochrome c with model membranes containing phosphatidylserine.
The effect of phosphatidylethanolamine (PE) on the binding of apocytochrome c to model membranes was examined. When 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) of the standard vesicles composed of 80% of this lipid and 20% of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoserine (POPS) was gradually replaced with upward of 50% of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), the binding increased appreciably. Ca(2+), causing the phase separation of PS, also brought about increased binding of apocytochrome c in the PC/PS system, underlining the importance of PS properties in membranes for the protein binding. The resonance energy transfer between Trp-59 in apocytochrome c and pyrene-PS incorporated into bilayers showed that the replacement of PC with PE increased the extent of apocytochrome c penetration into membranes by a PE concentration-dependent manner. However, in the absence of PS, PE had no apparent effect on these functions of apocytochrome c, suggesting that PE-induced change(s) of acidic membrane properties is important to the association of apocytochrome c with vesicles. From the observations that the excimer to monomer fluorescence ratio of pyrene-PS increased and the fluorescence of NBD-PS was quenched with increasing concentration of PE, it was deduced that PE caused PS-enriched domains in PC/PE/PS membranes. The colocalization of pyrene-PS with BODIPY-PS by PE further supported the possibility. We suggest that PE-induced formation of PS-enriched domains acts as binding sites for apocytochrome c in membranes.
Ahn
T
T
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, Korea.
Oh
D B
DB
Lee
B C
BC
Yun
C H
CH
D001059:Apoproteins / Q000378:metabolism*; D001692:Biological Transport; D003574:Cytochrome c Group / Q000378:metabolism*; D045304:Cytochromes c; D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D011485:Protein Binding
D001059:Apoproteins; D003574:Cytochrome c Group; D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D045304:Cytochromes c