Dynamical structure of the short multifunctional peptide BP100 in membranes

BP100 is a multifunctional membrane-active peptide of only 11 amino acids, with a high antimicrobial activity, an efficient cell-penetrating ability, and low hemolytic side-effects. It forms an amphiphilic α-helix, similar to other antimicrobial peptides like magainin. However, BP100 is very short and thus unlikely to form membrane-spanning pores as proposed for longer peptides as a mechanism of action. We thus studied the conformation, membrane alignment and dynamical behavior of BP100 in lipid bilayers (DMPC/DMPG), using oriented circular dichroism (OCD) and solid-state (19)F and (15)N NMR. According to OCD and (15)N NMR, the BP100 helix is oriented roughly parallel to the membrane surface, but these methods yield no information on the azimuthal alignment angle or the dynamics of the molecule. To address these questions, a systematic (19)F NMR analysis was performed, which was not straightforward for this short peptide. Only a limited number of positions could be (19)F-labeled, all of which are located on one face of the helix, which was found to lead to artifacts in the data analysis. It was nevertheless possible to reconcile the (19)F NMR data with the OCD and (15)N NMR data by using an advanced dynamical model, in which peptide mobility is described by fluctuating tilt and azimuthal angles with Gaussian distributions. (19)F NMR thus confirmed the regular α-helical conformation of BP100, revealed its azimuthal angle, and described its high mobility in the membrane. Furthermore, the very sensitive (19)F NMR experiments showed that the alignment of BP100 does not vary with peptide concentration over a peptide-to-lipid molar ratio from 1:10 to 1:3000.