On the interaction of the highly charged peptides casocidins with biomimetic membranes

Interdisciplinary-Inspired Smart Antibacterial Materials and Their Biomedical Applications

The discovery of antibiotics has saved millions of lives, but the emergence of antibiotic-resistant bacteria has become another problem in modern medicine. To avoid or reduce the overuse of antibiotics in antibacterial treatments, stimuli-responsive materials, pathogen-targeting nanoparticles, immunogenic nano-toxoids, and biomimetic materials are being developed to make sterilization better and smarter than conventional therapies. The common goal of smart antibacterial materials (SAMs) is to increase the antibiotic efficacy or function via an antibacterial mechanism different from that of antibiotics in order to increase the antibacterial and biological properties while reducing the risk of drug resistance. The research and development of SAMs are increasingly interdisciplinary because new designs require the knowledge of different fields and input/collaboration from scientists in different fields. A good understanding of energy conversion in materials, physiological characteristics in cells and bacteria, and bactericidal structures and components in nature are expected to promote the development of SAMs. In this review, the importance of multidisciplinary insights for SAMs is emphasized, and the latest advances in SAMs are categorized and discussed according to the pertinent disciplines including materials science, physiology, and biomimicry.

Why Do Tethered-Bilayer Lipid Membranes Suit for Functional Membrane Protein Reincorporation?

Membrane proteins (MPs) are essential for cellular functions. Understanding the functions of MPs is crucial as they constitute an important class of drug targets. However, MPs are a challenging class of biomolecules to analyze because they cannot be studied outside their native environment. Their structure, function and activity are highly dependent on the local lipid environment, and these properties are compromised when the protein does not reside in the cell membrane. Mammalian cell membranes are complex and composed of different lipid species. Model membranes have been developed to provide an adequate environment to envisage MP reconstitution. Among them, tethered-Bilayer Lipid Membranes (tBLMs) appear as the best model because they allow the lipid bilayer to be decoupled from the support. Thus, they provide a sufficient aqueous space to envisage the proper accommodation of large extra-membranous domains of MPs, extending outside. Additionally, as the bilayer remains attached to tethers covalently fixed to the solid support, they can be investigated by a wide variety of surface-sensitive analytical techniques. This review provides an overview of the different approaches developed over the last two decades to achieve sophisticated tBLMs, with a more and more complex lipid composition and adapted for functional MP reconstitution.

The antimicrobial peptides casocidins I and II: Solution structural studies in water and different membrane-mimetic environments

Antimicrobial peptides (AMPs) represent crucial components of the natural immune defense machinery of different organisms. Generally, they are short and positively charged, and bind to and destabilize bacterial cytoplasmic membranes, ultimately leading to cell death. Natural proteolytic cleavage of α_s2-casein in bovine milk generates the antimicrobial peptides casocidin I and II. In the current study, we report for the first time on a detailed structure characterization of casocidins in solution by means of Nuclear Magnetic Resonance spectroscopy (NMR). Structural studies were conducted in H₂O and different membrane mimetic environments, including 2,2,2-trifluoroethanol (TFE) and lipid anionic and zwitterionic vesicles. For both peptides, results indicate a mainly disordered conformation in H₂O, with a few residues in a partial helical structure. No wide increase of order occurs upon interaction with lipid vesicles. Conversely, peptide conformation becomes highly ordered in presence of TFE, with both casocidins presenting a large helical content. Our data point out a preference of casocidins to interact with model anionic membranes. These results are compatible with possible mechanisms of action underlying the antimicrobial activity of casocidins that ultimately may affect membrane bilayer stability.