Towards a molecular understanding of the membrane altering properties of viscosin, a cyclic lipodepsipeptide

Cyclic lipodepsipeptides (CLiPs) are a class of secondary metabolites produced by soil-borne bacteria such as Pseudomonas spp. that share a common blueprint, namely: a relative short oligopeptide sequence where the N-terminus is acylated with a fatty acid moiety. The ester bond establishes the macrocyclic nature by involving the C-terminus and a hydroxyl functionality. A great incentive for researching these unique molecules has been their pronounced biological activity profile. Aside from their beneficial traits to their natural ecological niche (e.g bioremediation, plant promoting potential,..) it was found that they offer tremendous potential in the fight against multi-resistant bacteria. Recently, their anticancer properties were demonstrated, fueling general interest. The wide applicability, in different biological settings and their amphipathic nature strongly suggests that the target of these peptides is the cellular membrane. Despite available biological data, the exact modus operandi of these compounds remains elusive. In this work, we will combine our access to synthetic variants of CLiPs with an arsenal of biophysical methodologies to monitor subtle structural changes occurring during the membrane binding. This will be made tangible by presenting an overview of Pseudomonas-CLiPs, with a subsequent zoom into the viscosin subgroup. Within our lab, an optimized synthesis strategy was developed, enabling us to introduce modifications in either the fatty acid moiety or in the peptidic backbone and subsequently monitor the impact of set alterations. Using a series of synthetic and natural viscosin members, we were able to pinpoint ‘activity hotspots' and to determine structural elements crucial for the observed activity. A highlight will be given of results obtained through liquid-state NMR, paramagnetic enhanced relaxation studies, molecular modelling but also in-depth analysis of the binding events occurring using Surface Plasmon Resonance (SPR) and Dual Polarization Interferometry (DPI)