Membrane insertion and lateral diffusion of fluorescence-labelled cytochrome c oxidase subunit IV signal peptide in charged and uncharged phospholipid bilayers

摘要: The synthetic 25-residue signal peptide of cytochrome c oxidase subunit IV was labelled with the fluorophor 7-nitrobenz-2-oxa-1,3-diazole (NBD) at its single cysteine residue. Addition small unilamellar vesicles 1-palmitoyl 2-oleoyl phosphatidylcholine (POPC) to resulted in a shift NBD excitation and emission spectra shorter wavelengths. Binding measured by increase fluorescence yield. A surface partition constant (3.9 +/- 0.5) x 10(3) M-1 derived from these titrations. When membrane contained, addition POPC, negatively charged phosphatidylglycerol (POPG), were further shifted wavelengths exhibited increased quantum yields. apparent constants 10(4)-10(5) for 20 or 100 mol% POPG. Lateral diffusion recovery after photobleaching multibilayers POPG, POPC/POPG (4:1) 1,2-dimyristoyl phosphatidylcholine. lateral coefficients bilayers POPC (8 10(-8) cm2/s 21 degrees C) 1.5-1.6-fold greater than those NBD-labelled phospholipids (5 C), but 1.5-1.8-fold smaller (3 20% POPG lipid bilayers. It is concluded that associates phospholipid two different forms, which depend on charge. experiments are well explained model partitions into region head-groups diffuses along membrane/water interface. If present membrane, electrostatic attractions between basic residues acidic result deeper penetration bilayer. For this case, models both consistent experimental data discussed, either forms an oligomer three six partially helical membrane-spanning monomers, inserts bilayer amphiphilic segment aligned parallel plane located near head-group outer hydrocarbon