Functional signal peptide reduces bilayer thickness of phosphatidylcholine liposomes

Abstract

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.

Selective Fluidization of Synaptosomal Plasma Membrane Vesicles by 17β-Estradiol

“…The R 0 value for the tryptophan-Py-3-Py donor-acceptor pair was 26.9 Å, which was comparable to the values for tryptophan-pyrene pair (Dobretsov et al, 1982;Tahara et al, 1992). In the calculation of R 0 , the value of k 2 was 2/3, and that of the (Schroeder et al, 1988;Sweet et al, 1987).…”

Distribution and Fluidizing Action of Soluble and Aggregated Amyloid β-Peptide in Rat Synaptic Plasma Membranes

“…Pyrene was then excited 1 min later through energy transfer from tryptophan (excitation ϭ 286 nm), and fluorescence emission spectra of pyrene were recorded. Considering that the Forster radius (the energy transfer-limiting distance) for the tryptophan-pyrene donor-acceptor pair is 3 nm (27), only pyrene located in the annular lipid (adjacent to proteins) was excited, and the fluidity of the annular lipid was considered proportional to the ratio F e /F m , where F e and F m are the fluorescence intensities of pyrene eximer (emission ϭ 480 nm) and monomer (emission ϭ 373 nm), respectively. Pyrene was then excited at 334 nm, and the bulk fluidity was considered to be proportional to the ratio F e /F m obtained with the 334-nm excitation wavelength.…”

“…This finding suggests that A␤ modulates membrane function by a nonreceptor-mediated mechanism, potentially as a result of altering the physico-chemical properties of membrane constituents, including lipids and proteins (13)(14)(15)(16). Indeed, previous membrane equilibrium binding experiments have demonstrated that the A␤ [25][26][27][28][29][30][31][32][33][34][35] fragment is highly lipophilic (K P Ͼ 10 2 ); the peptide intercalates deep into the membrane bilayer hydrocarbon core, as determined by small angle x-ray diffraction approaches (15). In addition, aggregated A␤ has strong electrostatic interactions with the surface of model membranes that appear to mediate its neurotoxicity (17).…”

“…A recent study from Cotman and co-workers (12) showed that A␤ neurotoxicity is independent of stereoisomerspecific ligand-receptor interaction because both all-D-and all-L-stereoisomers of A␤ [25][26][27][28][29][30][31][32][33][34][35] and A␤ had similar neurotoxic activity. This finding suggests that A␤ modulates membrane function by a nonreceptor-mediated mechanism, potentially as a result of altering the physico-chemical properties of membrane constituents, including lipids and proteins (13)(14)(15)(16).…”

Effect of a Decapeptide (VPDLLADLLK) on the Phase Transition of Dimyristoylphosphatidylcholine Lipid Bilayer

“…The thickness of the hydrophobic segment of the DMPC bilayer is around 29Å (21). The spacing between the phosphorous atom in the lipid headgroup and the first C atom of the acyl chain is about 5Å (22).…”