Dynamic Structure of Vesicle-Bound Melittin in a Variety of Lipid Chain Lengths by Solid-State NMR

Abstract

Solid-state 31P- and 13C-NMR spectra were recorded in melittin-lecithin vesicles composed of 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Highly ordered magnetic alignments were achieved with the membrane surface parallel to the magnetic field above the gel-to-liquid crystalline phase transition temperature (Tc). Using these magnetically oriented vesicle systems, dynamic structures of melittin bound to the vesicles were investigated by analyzing the 13C anisotropic and isotropic chemical shifts of selectively 13C-labeled carbonyl carbons of melittin under the static and magic-angle spinning conditions. These results indicate that melittin molecules adopt an alpha-helical structure and laterally diffuse to rotate rapidly around the membrane normal with tilt angles of the N-terminal helix being -33 degrees and -36 degrees and those of the C-terminal helix being 21 degrees and 25 degrees for DLPC and DPPC vesicles, respectively. The rotational-echo double-resonance method was used to measure the interatomic distance between [1-13C]Val8 and [15N]Leu13 to further identify the bending alpha-helical structure of melittin to possess the interhelical angles of 126 degrees and 119 degrees in DLPC and DPPC membranes, respectively. These analyses further lead to the conclusion that the alpha-helices of melittin molecules penetrate the hydrophobic cores of the bilayers incompletely as a pseudo-trans-membrane structure and induce fusion and disruption of vesicles.

Mechanical properties of lipid bilayers and regulation of mechanosensitive function

“…108 Moreover, the change in tilting observed in the TM segments of MS channels as a response to an increase in the lateral tension has also been described and simulated for Alm and melittin as a function of the equivalent bilayer hydrophobic thickness. 113,[122][123][124] As was anticipated, the main trend observed is that the tilt angles of these peptides increase with a reduction in lipid tail length in order to compensate positive HMs between the peptide length and bilayer thickness. 73,74,88 Studies with TM segments of proteins showing channel activity.…”

Melittin: a Membrane-active Peptide with Diverse Functions

“…At low concentrations, melittin adopts parallel orientation with respect to the membrane surface whereas when the concentration of peptide increases above a certain threshold value, an increasing fraction of peptide molecules change to the perpendicular orientation as explained by the two-state model for the action of antimicrobial peptides (Huang 2000). The orientation of a-helical segments of melittin in membranes is also found to be dependent on other important variables such as hydration, temperature and the phase state of the lipid (Vogel 1987;Frey and Tamm 1991;Toraya et al 2004). The sensitivity of these variables changes with the peptide and lipid.…”

“…In negatively charged lipids, fusion occurs under isothermal conditions (Morgan et al 1983). It has recently been shown in DPPC and DLPC bilayers that a-helices of melittin molecules penetrate the hydrophobic core of the bilayer incompletely as a pseudo-transmembrane structure, which could induce fusion and bilayer disruption (Toraya et al 2004). …”

“…4). The orientation of melittin in membranes is further complicated by the observation that melittin does not adopt a fully transmembrane orientation in membranes, but a pseudo-transmembrane orientation (Wall et al 1995;Bachar and Becker 2000;Toraya et al 2004). These studies therefore point out the role of lipid composition and the physical factors that affect the membrane properties in the orientation of melittin in membranes.…”

Recent Solid-State NMR Studies of Membrane-Bound Peptides and Proteins

“…2A and C) as evidenced by the axially symmetric pattern observed in DLPC-PG-1 [28] and DMPC-melittin bilayer systems ( Fig. 2[g]) [19,29]. When the spinning of the rotor stops, DMPC-melittin lipid-bilayer systems will spontaneously orient with the magnetic field, and the membranebound molecules also align with the magnetic field.…”