1-2-dilauroylphosphatidylcholine and protegrin-1

Antimicrobial peptides interact specifically with the membrane of a pathogen and kill the pathogen by releasing its cellular contents. Protegrin-1 (PG-1), a beta-hairpin antimicrobial peptide, is known to exist as a transmembrane monomer in a 1,2-dilauroylphosphatidylcholine (DLPC) bilayer and shows concentration-dependent oligomerization in a 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) bilayer. To examine its structure, dynamics, orientation, and interaction in membranes, we performed comparative molecular dynamics simulations of PG-1 monomer and dimer in DLPC and POPC bilayers for a total of 840 ns. The PG-1 monomer exhibits larger tilting in DLPC than in POPC due to a hydrophobic mismatch. PG-1 tilting is dependent on its rotation angle. The specific orientation of PG-1 in membranes is governed by the interactions of its aromatic residues with lipid headgroups. The calculated (15)N and (13)CO chemical shifts of Val(16) in DLPC reveal that there are different sets of tilt and rotation angles that satisfy the experimental values reasonably, suggesting that more experiments are needed to determine its orientation. The dimer simulations show that the dimer interface is better preserved in POPC than in DLPC because POPC's greater hydrophobic thickness causes reduced flexibility of the C-terminal strands. Both monomer and dimer simulations show membrane thinning around PG-1, largely due to arginine-lipid interactions.

Topics: Antimicrobial Cationic Peptides; Computer Simulation; Guanidine; Hydrogen Bonding; Hydrophobic and Hydrophilic Interactions; Lipid Bilayers; Models, Chemical; Models, Molecular; Nuclear Magnetic Resonance, Biomolecular; Phosphatidylcholines; Protein Multimerization; Protein Stability; Protein Structure, Secondary; Rotation; Water

All atom molecular dynamics simulations of the 18-residue beta-hairpin antimicrobial peptide protegrin-1 (PG-1, RGGRLCYCRRRFCVCVGR-NH(2)) in a fully hydrated dilauroylphosphatidylcholine (DLPC) lipid bilayer have been implemented. The goal of the reported work is to investigate the structure of the peptide in a membrane environment (previously solved only in solution [R.L. Fahrner, T. Dieckmann, S.S.L. Harwig, R.I. Lehrer, D. Eisenberg, J. Feigon, Solution structure of protegrin-1, a broad-spectrum antimicrobial peptide from porcine leukocytes. Chemistry and Biology, 3 (1996) 543-550]), and to delineate specific peptide-membrane interactions which are responsible for the peptide's membrane binding properties. A novel, previously unknown, "kick" shaped conformation of the peptide was detected, where a bend at the C-terminal beta-strand of the peptide caused the peptide backbone at residues 16-18 to extend perpendicular to the beta-hairpin plane. This bend was driven by a highly persistent hydrogen-bond between the polar peptide side-chain of TYR7 and the unshielded backbone carbonyl oxygen atom of GLY17. The H-bond formation relieves the unfavorable free energy of insertion of polar groups into the hydrophobic membrane core. PG-1 was anchored to the membrane by strong electrostatic binding of the protonated N-terminus of the peptide to the lipid head group phosphate anions. The orientation of the peptide in the membrane, and its influence on bilayer structural and dynamic properties are in excellent agreement with solid state NMR measurements [S. Yamaguchi, T. Hong, A. Waring, R.I. Lehrer, M. Hong, Solid-State NMR Investigations of Peptide-Lipid Interaction and Orientation of a b-Sheet Antimicrobial Peptide, Protegrin, Biochemistry, 41 (2002) 9852-9862]. Importantly, two simulations which started from different initial orientations of the peptide converged to the same final equilibrium orientation of the peptide relative to the bilayer. The kick-shaped conformation was observed only in one of the two simulations.

Topics: Anti-Infective Agents; Antimicrobial Cationic Peptides; Computer Simulation; Hydrogen Bonding; Lipid Bilayers; Models, Molecular; Phosphatidylcholines; Proteins

The influence of an antimicrobial peptide, protegrin-1 (PG-1), on the curvature and lateral diffusion coefficient (D(L)) of phosphocholine bilayers is investigated using one- (1D) and two-dimensional (2D) (31)P exchange NMR. The experiments utilize the fact that lipid lateral diffusion over the curved surface of vesicles changes the molecular orientation and thus the (31)P chemical shift anisotropy. This reorientation is manifested in 2D spectra as off-diagonal intensities and in 1D stimulated-echo experiments as reduced echo heights. The 2D spectra give information on the reorientation-angle distribution while the decay of the stimulated-echo intensity, which closely tracks the second-order correlation function in our experiments, yields the correlation times of the reorientation. The relationships among the 2D exchange spectra, stimulated-echo intensities, the correlation function, and reorientation-angle distributions are analyzed in detail. In the absence of PG-1, both dilaurylphosphotidylcholine (DLPC) and palmitoyloleoylphosphatidylcholine (POPC) vesicles show biexponential decays of the stimulated-echo intensities to equilibrium values of 0.20-0.25, suggesting that the curvature of the lipid vesicles has a bimodal distribution. The addition of PG-1 to DLPC vesicles increased the decay time constants, indicating that D(L) decreases due to peptide binding. In contrast, the addition of PG-1 to POPC vesicles decreased the decay constants by three to fivefold, indicating that the POPC vesicles are fragmented into smaller vesicles. On the basis of the changes in D(L) and the decay constants, we estimate that the radius of the POPC vesicles decreases by threefold due to PG-1 binding. Simulations of the 2D exchange spectra yielded quantitative reorientation-angle distributions that are consistent with the bimodal distributions of the vesicle curvature and the effects of the peptide on the two types of lipid bilayers. Thus, (31)P exchange NMR provides useful insights into the membrane morphological changes induced by this antimicrobial peptide.

Topics: Antimicrobial Cationic Peptides; Magnetic Resonance Spectroscopy; Membranes, Artificial; Phosphatidylcholines; Phosphorus Isotopes; Proteins; Sensitivity and Specificity; Time Factors