Table 1.
List of all the samples prepared for this study and their molecular composition.
Figure 1.
The materials and apparatus used for the experiment.
(a) Schematic representations of DMPC, DMPS, cholesterol, melatonin, amyloid- and amyloid-
molecules. (b) Diagram of the experimental setup used for the X-ray diffraction measurements. Two-dimensional data sets were collected to study molecular structure perpendicular to the solid supported membranes (out-of-plane) and parallel to the membranes (in-plane).
Figure 2.
Calculated electron distribution of A and A
.
The molecular structures and calculations are based on the PDB structures 1QWP (A) and 1IYT (A
). The peptides take helix-kink and helix-kink-helix configurations, respectively, in solution.
Figure 3.
Two-dimensional data for (a) DMPC +3 DMPS membrane, (b) DMPC/DMPS+3 mol% A
and (c) DMPC/DMPS+3 mol% A
.
The area per lipid is obtained from the position of the lipid acyl chain correlation peak at 1.5 Å−1.
Figure 4.
Reflectivity measurements for (a) DMPC/DMPS membrane, (b) DMPC/DMPS+3 mol% A, and (c) DMPC/DMPS+3 mol% A
.
Pronounced and equally spaced Bragg peaks were observed, which are indicative to a well ordered lamellar structure. Electron densities were calculated through Fourier transformation of the integrated peak intensities. The insets shows the function, which was used to assess the phases of the corresponding Fourier components.
Figure 5.
Electron density analyses obtained through Fourier transforms of the X-ray reflectivity data.
a) Electron densities for the DMPC/DMPS membrane (green), DMPC/DMPS+3 mol% A (blue), and DMPC/DMPS+3 mol% A
(red). b) The location of the A
peptide in the DMPC/DMPS membrane, as determined from the difference electron density profile peak positions. c) Gaussian fits to the difference electron density obtained by subtracting the electron density profile of the DMPC/DMPS sample from that of the DMPC/DMPS+3 mol% A
sample. A total of 4 peaks in each half of the bilayer are needed to fit the experimental data. The
-axis encompasses the full bilayer.
Table 2.
Parameters for the Gaussian fits to the A and A
distributions.
Figure 6.
Measured and calculated electron distribution of the membrane-embedded A a) and A
b) peptides and their position in the membrane.
Good agreement between calculations and experiments is obtained for a position of A in the hydrocarbon membrane core. The peptide takes a slightly tilted orientation, in agreement with computer simulations [85]. The full length A
peptide was also found to embed in anionic lipid exclude a membrane-spanning
-sheet structure, as it was reported from molecular dynamics simulations [82]–[84].
Figure 7.
Two-dimensional X-ray scans for the a) DMPC +3 mol% DMPS +30 mol% cholesterol and b) DMPC +3 mol% DMPS 3 mol% A+30 mol% cholesterol membranes.
Data were collected under full hydration of the membranes (100% RH), in their physiologically relevant fluid state.
Table 3.
Peak parameters for the fits to the in-plane cholesterol data shown in Figure 8.
Figure 8.
Reflectivity measurements for the a) DMPC/DMPS+30 mol% cholesterol membrane and the b) DMPC/DMPS+3 mol% A+30 mol% cholesterol membrane.
c) and d) show Lorentzian fits to corresponding in-plane data from Figures 7 c and d), scanned under 100 relative humidity. Note that Barrett et al. [56] identified the blue peaks as corresponding to in-plane features of crystalline cholesterol plaques. e) Cartoon of the structure of the multi-lamellar membrane complexes with membranes and coexisting cholesterol plaques and corresponding
-spacing. The cholesterol molecules in the plaques form a monoclinic lattice.
Figure 9.
Two-dimensional X-ray data for the a) DMPC/DMPS, b) DMPC/DMPS +30 mol% melatonin, and c) DMPC/DMPS +30 mol% melatonin +3 mol% A samples, with all scans done under full hydration.
Corresponding reflectivities are shown in d), e) and f). The phases can be determined from the function (shown as insets to the plots) and were used to determine the electron densities plotted in Figure 10.
Figure 10.
Electron densities for the a) DMPC/DMPS, b) DMPC/DMPS +30 mol% melatonin, and c) DMPC/DMPS +30 mol% melatonin +3 mol% A samples.
All samples were scanned under 100% RH. The difference in electron density in a) allows the determination of position of the melatonin molecules in the anionic lipid membranes. The location of the A peptide in the DMPC/DMPS+30 mol% melatonin membrane was determined from the difference electron density profile peak positions in b).
Table 4.
Composition and number of electrons of the different molecular components.
Table 5.
Parameters for the Gaussian fits to the A distributions for the melatonin-containing membrane.