Interaction of the antimicrobial peptides caerin 1.1 and aurein 1.2 with intact bacteria by 2 H solid-state NMR

Abstract

Nuclear magnetic resonance (NMR) is commonly used to probe the effect of antimicrobial agents on bacterial membranes using model membrane systems. Ideally, considering the complexity of membranes, the interaction of molecules with membranes should be studied in vivo. The interactions of two antimicrobial peptides (AMPs) with intact Escherichia coli and Bacillus subtilis were investigated using deuterium solid-state NMR. Specifically, we studied caerin 1.1 and aurein 1.2 isolated from the skin of Australian tree frogs. The minimal inhibitory concentration value for E. coli and B. subtilis was about 100μg/mL and 30μg/mL, respectively, for both peptides. A protocol to deuterate the membrane phospholipids of non-mutated B. subtilis was established using deuterated palmitic acid. H NMR spectra combined with spectral moment analysis support the interaction of the two AMPs with the hydrophobic core of the bacterial membranes. The presence of peptides decreased the order of the lipid acyl chains for both E. coli and B. subtilis, but at higher peptide concentrations for the Gram(+) bacteria. This may be explained by the presence of other cell wall components, such as the negatively-charged teichoic and lipoteichoic acids in the peptidoglycan, which would interact with the AMPs and decrease their actual concentration on the membrane surface. The mechanism of action of the AMPs thus depends on their local concentration as well as the membrane environment. The differences between the AMPs interaction with E. coli and B. subtilis reveal the importance of studying intact bacteria.

Interaction of the Antimicrobial Peptide Aurein 1.2 and Charged Lipid Bilayer

“…It is known that the peptide binding on the surface increases membrane area expansion, and disorders headgroup and acyl chain 3 , which is proportional to membrane tension 19, 29 . The transmembrane pore formation can be explained by the need to reduce membrane tension due to peptide binding on the surface, as the peptide insertion lessens membrane tension.…”

A New Method of Assessing Lipid Mixtures by 31P Magic-Angle Spinning NMR

“…Although PG is a ''lamellar-phase'' lipid, PE is known to transition from lamellar to inverse hexagonal phases depending on temperature. Detailed phase changes in lipid bilayers can be followed by measuring order-parameter variation in the hydrocarbon chains, using 2 H nuclear magnetic resonance (NMR) with labeled lipids, for example (5)(6)(7). However, lipid phases can also be quickly assessed without isotopic labeling, from static solid-state 31 P NMR spectra in natural-abundance membranes (8,9).…”

Magnetic-Alignment of Polymer Nanodiscs Probed by Solid-State NMR Spectroscopy

“…We believe that this study will be useful in optimizing the conditions that are needed to study membrane proteins reconstituted in polymer nanodiscs by solid-state NMR spectroscopy. [56][57][58][59][60] It is also worth mentioning that pH tolerance and deviant metal-ions resistance of SMA-QA polymer nanodiscs further expands the applications for solid-state NMR applications including structural studies on membrane proteins. In addition, as shown in our recent study, magnetically-aligned polymer macro-nanodiscs can be used to measure residual-dipolar-couplings by well-established solution NMR methods to study the structure and dynamics of water-soluble molecules including proteins, peptides, DNA, RNA and small molecule compounds.…”