Deuterium nuclear magnetic resonance investigation of the exchangeable sites on gramicidin A and gramicidin S in multilamellar vesicles of dipalmitoylphosphatidylcholine

Abstract

Solid gramicidin A and S and their interaction with DPPC bilayers were examined by 2H NMR as well as 31P NMR and differential scanning calorimetry (DSC). The deuterium spectra arose from deuterons associated with the peptide through chemical exchange in 2H2O. The spectra from both peptides were characterized by a quadrupolar splitting parameter, omega Q/2 pi approximately 150 kHz, and an asymmetry parameter, eta approximately 0.17. An additional 33 kHz, eta = 0 component arising from deuterons on mobile ornithine side chains was present in gramicidin S. In the gel phase of dipalmitoylphosphatidylcholine liposomes the gramicidins gave spectra that had components identical with those obtained from the solids. In the liquid-crystalline phase gramicidin A containing samples gave multicomponent spectra with a maximum quadrupolar splitting value of 133 kHz, eta = 0. A minimum in the T2e was observed, coinciding with the onset of the broadened phase transition measured by DSC and 31P NMR, due to the onset of axial rotation of the peptide in the bilayer. The different powder patterns in the liquid-crystalline spectra from gramicidin A probably arise from different amide sites along the transmembrane channel. The broad component of the 2H NMR spectra from gramicidin S in liposome preparations was not affected by the lipid-phase transition. The T2e was also constant over this temperature range. The results are consistent with a location of gramicidin S at the membrane surface.

The conducting form of gramicidin A is a right-handed double-stranded double helix

“…Three major multiresonance peaks have been attributed to NOH bonds making angles of 15°, 25°, and 39°with the direction of the magnetic field perpendicular to the bilayer normal. In a related study using 2 H-labeled gramicidin, similar results also were obtained (16). The six crystallographically independent strands in the structures reported here provide information on the range of stable orientations of individual NOH bonds in the dimer.…”

NMR methods for studying membrane‐active antimicrobial peptides

“…There is a fundamental difference in lipid composition between bacterial and eukaryotic membranes. Eukaryotic plasma membranes contain a (195) 1986 Gramicidin S 1 pulse 31 P No DPPC (196) 1988 Gramicidin S Quad echo; 1 pulse (75°) 2 H; 31 P Acyl chain; no DMPC, DMPC-d 54 (197) 1997 Gramicidin S high amount of phosphatidylcholine (PC) and cholesterol, which are mostly absent in bacteria. On the other hand, bacterial membranes are rich in phosphatidylethanolamine (PE) and phosphatidylglycerol (PG), which constitute only a small fraction in eukaryotes.…”

Characterization of dynamic processes using deuterium in uniformly 2H,13C,15N enriched peptides by MAS solid-state NMR

“…Brown and coworkers [33] described a novel method which correlates 2 H NMR relaxation rates and order parameter calculations to understand the forces associated with bilayer deformation. With respect to membrane proteins, deuterium experiments describing dynamical properties of gramicidin A and S incorporated into liposomes were carried out by Dameta et al [34]. Cross and co-workers [35] extended this approach and, e.g., determined the dynamics and structural properties for each of the valine side chains of oriented and amorphous gramicidin solubilized in hydrated lipid bilayers.…”