Recent progress on the application of 2H solid-state NMR to probe the interaction of antimicrobial peptides with intact bacteria.

Discoveries relating to innate immunity and antimicrobial peptides (AMPs) granted Bruce Beutler and Jules Hoffmann a Nobel prize in medicine in 2011, and opened up new avenues for the development of therapies against infections, and even cancers. The mechanisms by which AMPs interact with, and ultimately disrupt, bacterial cell membranes is still, to a large extent, incompletely understood. Up until recently, this mechanism was studied using model lipid membranes that failed to reproduce the complexity of molecular interactions present in real cells comprising lipids but also membrane proteins, a cell wall containing peptidoglycan or lipopolysaccharides, and other molecules. In this review, we focus on recent attempts to study, at the molecular level, the interaction between cationic AMPs and intact bacteria, by 2H solid-state NMR. Specifically-labeled lipids allow us to focus on the interaction of AMPs with the heart of the bacterial membrane, and measure the lipid order and its variation upon interaction with various peptides. We will review the important parameters to consider in such a study, and summarize the results obtained in the past 5years on various peptides, in particular aurein 1.2, caerin 1.1, MSI-78 and CA(1-8)M(1-10). This article is part of a Special Issue entitled: Biophysics in Canada, edited by Lewis Kay, John Baenziger, Albert Berghuis and Peter Tieleman.

Protocols for Studying the Interaction of MSI-78 with the Membranes of Whole Gram-Positive and Gram-Negative Bacteria by NMR.

Antimicrobial peptides (AMPs) may interact with a variety of target cell components, including the lipid bilayer, non-lipidic cell envelope components, and/or intracellular targets. However, most biophysical experiments aimed at elucidating the detailed mechanism of AMPs are limited to simple model membrane systems and neglect potentially functional interactions between AMPs and non-lipidic cell components. One of the biophysical techniques commonly used to study how AMPs interact with lipid bilayers is solid-state deuterium NMR. In this chapter we provide protocols to prepare deuterium-labeled intact Gram-negative and Gram-positive bacteria and to observe these samples using solid-state deuterium NMR. Such experiments have the potential to provide important information about how non-lipidic cell envelope components modulate AMP interactions with the cytoplasmic membrane of bacteria.