Orientation and pore-forming mechanism of a scorpion pore-forming peptide bound to magnetically oriented lipid bilayers

The orientation and pore-forming mechanisms of pandinin 2 (pin2), an antimicrobial peptide isolated from venom of the African scorpion Pandinus imperator, bound to magnetically oriented lipid bilayers were examined by P-31 and C-13 solid-state, and N-15 liquid-state NMR spectroscopy. P-31 NMR measurements at various temperatures, under neutral and acidic conditions, showed that membrane lysis occurred only under acidic conditions, and at temperatures below the liquid crystal-gel phase transition of the lipid bilayers, after incubation for two days in the magnet. Differential scanning calorimetry measurements showed that pin2 induced negative curvature strain in lipid bilayers. The C-13 chemical shift values of synthetic pin2 labeled at Gly(3), Gly(8), Leu(12), Phe(17), or Ser(18) under static or slow magic-angle spinning conditions, indicate that pin2 penetrates the membrane with its average helical axis perpendicular to the membrane surface. Furthermore, amide H-D exchange experiments of N-15-Ala(4), Gly(8), and Ala(9) triply-labeled pin2 suggest that this peptide forms oligomers and confirms that the N-terminal region creates membrane pores.