Cyclic lipopeptides (CLiPs) are a versatile group of secondary metabolites with antibacterial, antiviral, antifungal, and anticancer activity. Produced by bacteria, such as Pseudomonas , Bacillus , or Streptomyces , CLiPs show an amphiphilic character that is determined by a cyclic oligopeptide group linked to a lipid tail. This amphiphilicity drives interactions with membranes, which are often fundamental to their mode of action. Our research investigates these interactions, focusing on (1) the binding mechanism of CLiPs to membranes, and (2) the relationship between their structure and membrane-permeabilizing activity. (1) We first examine the binding mechanism of a novel CLiP, olikomycin A, derived from Streptomyces species. We characterize membrane binding using isothermal titration calorimetry (ITC). Symmetric or asymmetric liposomes and electroneutral polymer-based nanodiscs are used as model membranes. We address questions regarding the binding stoichiometry, the flipping process, and propose an initial hypothetical model of the membrane binding process of olikomycin A. To contextualize our new CLiP within the ongoing fight against global antibiotic resistance, we also present a comprehensive analysis of daptomycin, the only CLiP currently used clinically. (2) Second, we investigate the relationship between the structure and membrane-permeabilizing activity using a third CLiP, tolaasin I, produced by Pseudomonas tolaasii . The impact of cyclization was examined using a time-resolved fluorescence assay, including the self-quenching dye calcein. This leakage assay enables us to compare membrane permeabilization of tolaasin I with its linear, inactive analogue, while discussing separately membrane partitioning and local damage. Together, these studies provide detailed insights into how CLiPs interact with membranes and how structural features such as cyclization influence their activity. This knowledge expands our understanding of CLiP mechanisms and may support the rational design of new membrane-targeting compounds.
Crocoll et al. (2026) studied this question.