Tilted peptides

Fig. 8.2 Time development of two systems. On A and B is linear tilted peptide (L ) in the membrane in LC state on C and D is peptide (V ) nearly perpendieular to membrane, but it is bended...

System Angle P and 2" half Tilt (°) Peptide s effeetive thiekness Full peptide s length (nm) Membrane s effeetive thiekness ... 

Fantini J, Carlus D, Yahi N. The fusogenic tilted peptide (67-78) of alpha-s)muclein is a cholesterol binding domain. Biochim Biophys Acta. 2011 1808(10) 2343-2351. 

Lins L, Brasseur R. Tilted peptides a structural motif involved in protein membrane insertion / Pept Sci. 2008 14(4) 416-422. 

Brasseur R. Tilted peptides a motif for membrane destabilization (hypothesis). Mol Memhr Biol. 2000 17(1) 31 0. 

Di Scala C, Yahi N, Lelievre C, Garmy N, Chahinian H, Fantini J. Biochemical identification of a linear cholesterol-binding domain within Alzheimer s beta amyloid peptide. ACS Chem Neurosd. 2013 4(3) 509-517. Fantini J, Carlus D, Yahi N. The fusogenic tilted peptide (67-78) of alpha-syimdein is a cholesterol binding domain. Biochim Biophys Acta. 2011 1808(10) 2343-2351. 

Fig. 1 Solid-state NMR structure analysis relies on the 19F-labelled peptides being uniformly embedded in a macroscopically oriented membrane sample, (a) The angle (0) of the 19F-labelled group (e.g. a CF3-moiety) on the peptide backbone (shown here as a cylinder) relative to the static magnetic field is directly reflected in the NMR parameter measured (e.g. DD, see Fig. 2c). (b) The value of the experimental NMR parameter varies along the peptide sequence with a periodicity that is characteristic for distinct peptide conformations, (c) From such wave plot the alignment of the peptide with respect to the lipid bilayer normal (n) can then be evaluated in terms of its tilt angle (x) and azimuthal rotation (p). Whole-body wobbling can be described by an order parameter, S rtlo. (d) The combined data from several individual 19F-labelled peptide analogues thus yields a 3D structural model of the peptide and how it is oriented in the lipid bilayer...

In summary, we may thus conclude that PGLa and GS do not form stable, NMR-observable pores in native membrane as readily as they do in model bilayers. The corresponding tilted and/or inserted states of our two representative MAPs could only be comprehensively characterized in DMPC-based samples, where the peptides could be trapped in a uniform state. In living cells, on the other hand, these states would seem to be only of a transient nature, i.e. at the very moment when the antimicrobial peptide attacks the membrane and passes through the lipid barrier along its concentration gradient towards the cytosol. 

The peptide alignment is calculated by a / -analysis of the F-NMR chemical shifts as a function of r and p (using Smoi = 1 as there is no wobble), as previously explained [18,19,22,23]. Figure 5A,B shows the allowed regions in the r-p maps for GS-3/3 and GS-l/T, respectively. The overlap of the allowed regions suggests a peptide tilt angle r between 70° and 90°, but the value of the azimuthal rotation p is not well defined. 

Fig. 5 Contour plots showing the alignment of gramicidin S in DMPC membranes at high peptidedipid ratios (>1 40), evaluated in terms of the peptide tilt angle x and its azimuthal rotation p. Feasible solutions from F-NMR of GS-3/3 (A) and GS-1/1 (B) are shown, together with additional N-NMR constraints from GS-3/3 (C) and GS-1/1 (D). A unique overlap is obtained at t 80° and p -45°, as indicated by the shaded dots...

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. 

MacKinnon, who was awarded the 2003 Nobel Prize in Chemistry, has recently provided the first in-depth experimental structure of an ion-selective channel. He studied a transmembrane K+ channel composed of four identical subunits clustered symmetrically around a central pore. Each subunit contributes two membrane-traversing a-helices, which are connected by a peptide loop, called the P-region, that constitutes the selectivity filter of the channel. These two a-helices are tilted away from the central axis towards the extracellular side of the channel. Four inner a-helices from each of the subunits line the pore toward the cytoplasmic end. The inner and outer mouths of the pore are lined with amino acid side chains. The selectivity filter is lined by three main-chain carbonyl groups from the protein backbone of each of the four subunits. The channel is occupied by three K+ atoms. 

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