title: High-resolution structures and orientations of antimicrobial peptides piscidin 1 and piscidin 3 in fluid bilayers reveal tilting, kinking, and bilayer immersion.
abstract: While antimicrobial peptides (AMPs) have been widely investigated as potential therapeutics, high-resolution structures obtained under biologically relevant conditions are lacking. Here, the high-resolution structures of the homologous 22-residue long AMPs piscidin 1 (p1) and piscidin 3 (p3) are determined in fluid-phase 3:1 phosphatidylcholine/phosphatidylglycerol (PC/PG) and 1:1 phosphatidylethanolamine/phosphatidylglycerol (PE/PG) bilayers to identify molecular features important for membrane destabilization in bacterial cell membrane mimics. Structural refinement of (1)H-(15)N dipolar couplings and (15)N chemical shifts measured by oriented sample solid-state NMR and all-atom molecular dynamics (MD) simulations provide structural and orientational information of high precision and accuracy about these interfacially bound α-helical peptides. The tilt of the helical axis, τ, is between 83° and 93° with respect to the bilayer normal for all systems and analysis methods. The average azimuthal rotation, ρ, is 235°, which results in burial of hydrophobic residues in the bilayer. The refined NMR and MD structures reveal a slight kink at G13 that delineates two helical segments characterized by a small difference in their τ angles (<10°) and significant difference in their ρ angles (~25°). Remarkably, the kink, at the end of a G(X)4G motif highly conserved among members of the piscidin family, allows p1 and p3 to adopt ρ angles that maximize their hydrophobic moments. Two structural features differentiate the more potent p1 from p3: p1 has a larger ρ angle and less N-terminal fraying. The peptides have comparable depths of insertion in PC/PG, but p3 is 1.2 Å more deeply inserted than p1 in PE/PG. In contrast to the ideal α-helical structures typically assumed in mechanistic models of AMPs, p1 and p3 adopt disrupted α-helical backbones that correct for differences in the amphipathicity of their N- and C-ends, and their centers of mass lie ~1.2-3.6 Å below the plane defined by the C2 atoms of the lipid acyl chains.
authors.affiliation: Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health , Bethesda, Maryland 20892, United States.
authors.forename: B Scott
authors.initials: BS
authors.lastname: Perrin
authors.forename: Ye
authors.initials: Y
authors.lastname: Tian
authors.forename: Riqiang
authors.initials: R
authors.lastname: Fu
authors.forename: Christopher V
authors.initials: CV
authors.lastname: Grant
authors.forename: Eduard Y
authors.initials: EY
authors.lastname: Chekmenev
authors.forename: William E
authors.initials: WE
authors.lastname: Wieczorek
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Dao
authors.forename: Robert M
authors.initials: RM
authors.lastname: Hayden
authors.forename: Caitlin M
authors.initials: CM
authors.lastname: Burzynski
authors.forename: Richard M
authors.initials: RM
authors.lastname: Venable
authors.forename: Mukesh
authors.initials: M
authors.lastname: Sharma
authors.forename: Stanley J
authors.initials: SJ
authors.lastname: Opella
authors.forename: Richard W
authors.initials: RW
authors.lastname: Pastor
authors.forename: Myriam L
authors.initials: ML
authors.lastname: Cotten
mesh_terms: D023181:Antimicrobial Cationic Peptides / Q000737:chemistry*; D029941:Fish Proteins / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D007101:Immersion; D008051:Lipid Bilayers / Q000737:chemistry*; D050866:Liquid Crystals / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D017433:Protein Structure, Secondary
chemical_list: D023181:Antimicrobial Cationic Peptides; D029941:Fish Proteins; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; C449802:moronecidin protein, Morone saxatilis