Synergistic Activity of Antimicrobial Peptides

(supported by the Austrian Science Fund, Project No. I 1763)

start of project: 01. 03. 2015
end of project: 31. 08. 2018

Antibiotic-resistant bacterial strains represent a global health problem with a strong social and economic impact. Because of increasing antibiotic resistance against conventional antibiotics, there is an urgent need for the development of antibiotics with novel mechanisms of action.

Significant research efforts have been devoted to antimicrobial peptides, because they interfere physically with the cell membrane of bacteria and offer a fast killing, non-receptor-mediated defense against invading pathogens. Of particular interest is the observation of synergistic activity of antimicrobial peptides, i.e. application of mixtures of antimicrobial peptides shows larger effects than the sum of individual applications. However, a quantitative understanding of peptide synergism is lacking at large. The aim of the project is to derive the quantitative physicochemical foundations pertaining to this effect. A specific focus of the project is on the role of the bacterial membrane and its structural and dynamic coupling to peptides. Previous data suggests that synergism arises from a preconditioning of the membrane by one peptide, which helps the insertion and membrane perturbation by the second peptide. We will combine a unique complementary set of experimental and theoretical tools to master the aims of the project. In particular we will apply (i) X-ray/neutron scattering to derive the structural and elastic response of bacterial membrane mimics, including peptide induced membrane domains, (ii) solid-state NMR to determine accurately the location and orientation (topology) of these peptides in aligned membranes, including peptide aggregation and dynamics and (iii) molecular dynamics simulations to gain atomistic insight on the molecular interactions involved. The application involves the development of new methods, such as the deconvolution of the dynamics of membrane bound peptides, as well as correlating the motions of peptides and lipids in membrane environments using solid-state NMR spectroscopy. The combination of all data will provide a complete picture of the physical events and the underlying modes of action with methodological improvements that can be applied to lipid/peptide interactions in general.

Specifically, we will study mixtures of PGLa and magainin 2, antimicrobial peptides from frog skin, as well as the naturally occurring heterodimer distinctin and homodimer homotarsinin. Further, we will study chemically linked PGLa and magainin 2. In doing so, we will address the differential effects of crosslinking of like or unlike peptide helices and their physical relation to peptide synergism. Further this allows us also to address the question whether or not peptide synergism is achieved through peptide pair formation.

It is expected that this project will lead to ground breaking scientific knowledge that will enable us to establish molecular mechanism(s) for the synergistic activity of antimicrobial peptides as an indispensable prerequisite for the future design of new more potent therapeutic approaches against bacteria