Membrane normal

Figure 13.6. From left to right location of the P-amyloid region of amyloid precursor protein (APP) in relation to the neuronal membrane normal processing of APP inactivates P-amyloid abnormal processing of APP in Alzheimer s disease liberates intact P-amyloid.

Another approach to explain tubule formation was taken by Lubensky and Prost as part of a general theoretical study of the relationship between orientational order and vesicle shape.173 These authors note that a membrane in an Lp/ phase has orientational order within the membrane which is lacking in the La phase. The clearest source of orientational order is the tilt of the molecules with respect to the local membrane normal The molecules select a particular tilt direction, and hence the local elastic properties of the membrane become anisotropic. A membrane might also have other types of orientational order. For example, if it is in a hexatic phase, it has order in the orientations of the intermolecular bonds (not chemical bonds but lines indicating the directions from one molecule to its nearest neighbors in the membrane). 

The first approach has successfully been applied to the study of amorphous as well as to macroscopically ordered solids. Examples of applications include the determination of backbone geometries in fibrous proteins [4] or the determination of protein-backbone, side-chain, and bound-ligand orientation with respect to the membrane normal in membrane-bound proteins [5-8]. Membranes, bilayers, bicelles, or liposomes are neither solid nor liquid systems but have aspects of both and are sometimes liquid crystalline. In most of these systems, time-independent anisotropic interactions play an important role,... 

Figure 45 illustrates how all the different methyl group orientations with respect to the membrane normal N are accommodated in space by the proposed structure of retinal within bR. This picture is clear from the measured values of 9, which are indicated as labels to the individual methyl groups. The roughly parallel orientations of the two methyl groups, C18 (9 = 37°) and C19 (9 = 40°), demonstrate that retinal must have a... 

FIGURE 45. Orientation and conformation of retinal in bR, constructed from the individual methyl group orientations that have been determined by solid-state 2H NMR. The angles 6 of the C—CD3 bond vectors with respect to the membrane normal (N) were evaluated for Cis (37°), C49 (40°) and C20 (32°) from the zero-tilt spectra shown in Figure 44 and with the aid of line-shape simulation of the tilt series in Figure 42 and 43. Reprinted with permission from Reference 57. Copyright (1994) American Chemical Society... 

Although fusion between SFV and the plasma membrane normally does not occur, cell surface-bound viruses can be induced to fuse simply by decreasing the extracellular pH below 6 for a few seconds (White et al., 1980 Vaananen et al., 1981). As a result of its fusion activity SFV can hemolyze red blood cells at pH 5.8 (VaanSnen and Kaari inen, 1979, 1980). However, the lysis occurs only with virus damaged by freezing and thawing. Cells can also be made to fuse with each other using SFV at low pH (White et al., 1981). 

TUt angle of the peptide symmetry axis with respect to the membrane normal Azimuthal rotation angle of the peptide Molecular order parameter of the peptide... 

Fig.3 -NMR spectra at different sample orientations. The oriented sample of Fig. 2B was manually tilted in the static magnetic field Bq to acquire spectra at different angles, where 0 = 0° corresponds to the usual alignment of the sample normal parallel to the direction of Bq. The arrows indicate the shift of the anisotropic signals with respect to the isotropic value (dotted line), according to the factor 3(cos - l)/2 as expected for a molecule undergoing fast long-axial rotation about the membrane normal...

Based on the N-NMR data alone, the corresponding areas in the x-p maps are displayed in Fig. 5C ( N-Val in GS-3/30 and Fig. 5D ( N-Leu in GS-l/lO. The overlap of these regions with the constraints from F-NMR (Fig. 5A,B) thus defines the novel orientation of gramicidin S in membranes at high peptide concentration. The allowed area (common to all four panels) is marked by a dot in Fig. 5 at r = 80° 10° and p = -45° 10. As the value of r is close to a right angle between the molecular symmetry axis (z-axis, see Fig. 1) and the membrane normal, this means that the P-sheet plane (x-y plane) is tilted almost perpendicular with respect to the lipid bilayer plane. The value of p indicates that the P-strands (peptide /-axis) are inclined by about 45° with respect to the membrane normal. 

The subunit pmoC, colored red in Figure 7.51, is comprised of five TM a-helices that are oriented approximately parallel to the membrane normal and to each other. A single zinc metal ion, in a distorted tetrahedral coordination sphere, has been modeled within the membrane. Conserved amino acid resi-... 

Fig. 3.3 Infrared spectra with attenuated total reflectance using polarized light for lipid A from E.coli and from Rhodobacter capsulatus. The two lipid A have identical backbone structures, but differences in the acylation pattern. As can be seen, the vibrational bands corresponding to diglucosamine ring vibrations have different dichroic ratios, which is indicative for a different inclination of the backbones with respect to the membrane normal...

---