Functional signal peptide reduces bilayer thickness of phosphatidylcholine liposomes.
To investigate the interaction between a signal peptide and the lipid bilayer, two kinds of peptides, L8-M5 (L8 = MRL8PLAALG, M5 = KVFER) and L14-M5 (L14 = MRL14PLAALG), were examined in membranes composed of dioleoylphosphatidylcholine (DOPC). Peptides L8 and L14 are artificially designed signal sequences, and M5 is the N-terminal five residues of human lysozyme; L8 mediated effective secretion of human lysozyme in yeast, while L14 did not [Yamamoto, Y., et al. (1987) Biochem. Biophys. Res. Commun. 149, 431-436]. DOPC liposomes incorporating L8-M5 or L14-M5 were observed by electron cryomicroscopy as pairs of concentric circles, and the separation of the bilayer was measured along the membrane. Peptide L8-M5 was found to reduce the bilayer thickness, but L14-M5 did not. CD measurements revealed that L8-M5 adopted an alpha-helical conformation with random coil in the liposome membranes and that L14-M5 adopted a more helical and less random conformation than L8-M5. Fluorescence spectroscopy using both aqueous and membranous probes revealed that L8-M5 destabilized the lipid bilayer more strongly than L14-M5. These results suggest that functional L8-M5 reduces the bilayer thickness and destabilizes the lipid bilayer and that these activities are important for signal peptide function.
Tahara
Y
Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Murata
M
M
Ohnishi
S
S
Fujiyoshi
Y
Y
Kikuchi
M
M
Yamamoto
Y
Y
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes; D008567:Membranes, Artificial; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry*; D011487:Protein Conformation; D021382:Protein Sorting Signals / Q000737:chemistry*; D012995:Solubility; D013050:Spectrometry, Fluorescence
D008051:Lipid Bilayers; D008081:Liposomes; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D021382:Protein Sorting Signals