Pore structure, thinning effect, and lateral diffusive dynamics of oriented lipid membranes interacting with antimicrobial peptide protegrin-1: 31P and 2H solid-state NMR study

Structure of chemokine-derived antimicrobial Peptide interleukin-8alpha and interaction with detergent micelles and oriented lipid bilayers

Interleukin-8alpha (IL-8alpha) is an antimicrobial peptide derived from the chemokine IL-8. Solution NMR was used to determine the atomic-resolution structure of IL-8alpha in SDS micelles. Solid-state NMR and tryptophan fluorescence were used to probe the interaction of IL-8alpha with model membranes. The peptide interacted differently with anionic versus purely zwitterionic micelles or bilayers. Tryptophan fluorescence demonstrated a deeper position of Trp4 in SDS micelles and POPC/POPG bilayers compared to pure POPC bilayers, consistent with (2)H order parameters, which also indicated a deeper position of the peptide in POPC/POPG bilayers compared to POPC bilayers. Paramagnetic probe data showed that IL-8alpha was situated roughly parallel to the SDS micelle surface, with a slight tilt that positioned the N-terminus more deeply in the micelle compared to the C-terminus. (15)N solid-state NMR spectra indicated a similar, nearly parallel position for the peptide in POPC/POPG bilayers. (31)P and (2)H solid-state NMR demonstrated that the peptide did not induce the formation of any nonlamellar phases and did not significantly disrupt bilayer orientation in aligned model membranes composed of POPC or POPC and POPG.

Beyond NMR spectra of antimicrobial peptides: dynamical images at atomic resolution and functional insights

There is a considerable current interest in understanding the function of antimicrobial peptides for the development of potent novel antibiotic compounds with a very high selectivity. Since their interaction with the cell membrane is the major driving force for their function, solid-state NMR spectroscopy is the unique method of choice to study these insoluble, non-crystalline, membrane-peptide complexes. Here I discuss solid-state NMR studies of antimicrobial peptides that have reported high-resolution structure, dynamics, orientation, and oligomeric states of antimicrobial peptides in a membrane environment, and also address important questions about the mechanism of action at atomic-level resolution. Increasing number of solid-state NMR applications to antimicrobial peptides are expected in the near future, as these compounds are promising candidates to overcome ever-increasing antibiotic resistance problem and are well suited for the development and applications of solid-state NMR techniques.

Structure and membrane interactions of the antibiotic peptide dermadistinctin K by multidimensional solution and oriented 15N and 31P solid-state NMR spectroscopy

DD K, a peptide first isolated from the skin secretion of the Phyllomedusa distincta frog, has been prepared by solid-phase chemical peptide synthesis and its conformation was studied in trifluoroethanol/water as well as in the presence of sodium dodecyl sulfate and dodecylphosphocholine micelles or small unilamellar vesicles. Multidimensional solution NMR spectroscopy indicates an alpha-helical conformation in membrane environments starting at residue 7 and extending to the C-terminal carboxyamide. Furthermore, DD K has been labeled with (15)N at a single alanine position that is located within the helical core region of the sequence. When reconstituted into oriented phosphatidylcholine membranes the resulting (15)N solid-state NMR spectrum shows a well-defined helix alignment parallel to the membrane surface in excellent agreement with the amphipathic character of DD K. Proton-decoupled (31)P solid-state NMR spectroscopy indicates that the peptide creates a high level of disorder at the level of the phospholipid headgroup suggesting that DD K partitions into the bilayer where it severely disrupts membrane packing.

Evidence of pores and thinned lipid bilayers induced in oriented lipid membranes interacting with the antimicrobial peptides, magainin-2 and aurein-3.3

Dynamic structures of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers induced in oriented lipid membranes, which are interacting with membrane-acting antimicrobial peptides (AMPs), magainin-2 and aurein-3.3, were explored by 31P and 2H solid-state NMR (ssNMR) spectroscopy. Various types of phospholipid systems, such as POPC-d31, POPC-d31/POPG, and POPC-d31/cholesterol, were investigated to understand the membrane disruption mechanisms of magainin-2 and aurein-3.3 peptides at various peptide-to-lipid (P:L) ratios. The experimental lineshapes of anisotropic 31P and 2H ssNMR spectra measured on these peptide-lipid systems were simulated reasonably well by assuming the presence of supramolecular lipid assemblies, such as toroidal pores and thinned bilayers, in membranes. Furthermore, the observed decrease in the anisotropic frequency span of either 31P or 2H ssNMR spectra of oriented lipid bilayers, particularly when anionic POPG lipids are interacting with AMPs at high P:L ratios, can directly be explained by a thinned membrane surface model with fast lateral diffusive motions of lipids. The spectral analysis protocol we developed enables extraction of the lateral diffusion coefficients of lipids distributed on the curved surfaces of pores and thinned bilayers on a few nanometers scale.