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

Faculty of Engineering, Yokohama National University, Yokohama, Japan

Correspondence: Address reprint requests to Akira Naito, E-mail address: naito{at}ynu.ac.jp.

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 (T_c). 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 -helical structure and laterally diffuse to rotate rapidly around the membrane normal with tilt angles of the N-terminal helix being –33° and –36° and those of the C-terminal helix being 21° and 25° 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 -helical structure of melittin to possess the interhelical angles of 126° and 119° in DLPC and DPPC membranes, respectively. These analyses further lead to the conclusion that the -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.

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