Structure and Orientation of Bovine Lactoferrampin in the Mimetic Bacterial Membrane as Revealed by Solid-State NMR and Molecular Dynamics Simulation

Bovine lactoferrampin (LFampinB) is a newly discovered antimicrobial peptide found in the N1-domain of bovine lactoferrin (268-284), and consists of 17 amino-acid residues. It is important to determine the orientation and structure of LFampinB in bacterial membranes to reveal the antimicrobial mechanism. We therefore performed C-13 and P-31 NMR, C-13-P-31 rotational echo double resonance (REDOR), potassium ion-selective electrode, and quartz-crystal microbalance measurements for LFampinB with mimetic bacterial membrane and molecular-dynamics simulation in acidic membrane. P-31 NMR results indicated that LFampinB caused a defect in mimetic bacterial membranes. Ion-selective electrode measurements showed that ion leakage occurred for the mimetic bacterial membrane containing cardiolipin. Quartz-crystal microbalance measurements revealed that LFampinB had greater affinity to acidic phospholipids than that to neutral phospholipids. C-13 DD-MAS and static NMR spectra showed that LFampinB formed an alpha-helix in the N-terminus region and tilted 45 degrees to the bilayer normal. REDOR dephasing patterns between carbonyl carbon nucleus in LFampinB and phosphorus nuclei in lipid phosphate groups were measured by C-13-P-31 REDOR and the results revealed that LFampinB is located in the interfacial region of the membrane. Molecular-dynamics simulation showed the tilt angle to be 42 degrees and the rotation angle to be 92.5 degrees for Leu(3), which are in excellent agreement with the experimental values.