Abstract

The lateral organization of lipids into distinct domains, often referred to as **lipid rafts**, is a fundamental characteristic of biological membranes that is crucial for various cellular processes, including signal transduction and protein sorting. This study investigates the **interaction of ordered lipid domains** in model membranes, specifically focusing on the influence of **amphipathic peptides**. Amphipathic peptides are known to interact strongly with the lipid bilayer, often mediating membrane fusion, pore formation, or antimicrobial activity. Using a combination of **fluorescence microscopy** and **atomic force microscopy (AFM)** on phase-separated giant unilamellar vesicles (GUVs), we quantitatively assessed the changes in domain size, shape, and boundary tension upon the incorporation of a model amphipathic peptide. Our results demonstrate that the peptide preferentially partitions into the disordered phase but significantly alters the physical properties of the ordered domains, leading to a **reduction in domain-domain repulsion** and an increase in domain coalescence. This effect is concentration-dependent and suggests a mechanism by which these peptides can modulate membrane heterogeneity and function. These findings provide critical insights into the physical principles governing membrane organization and the molecular basis for peptide-membrane interactions in cell biology.