A Versatile GPMV-Imaging Platform for Quantitative Analysis of Receptor Binding and Membrane Fusion

Membrane fusion is central to biological processes such as viral entry, fertilization and cell-to-cell fusion. Gaining a mechanistic understanding of fusion requires the ability to visualize and quantify the dynamic interaction between two membranes and their associated protein machineries at high temporal and spatial resolution. However, studying these processes in live cells remains challenging due to the complexity of the cellular environment. Here we demonstrate a versatile cell-free platform based on giant plasma membrane vesicles (GPMVs) that enables controlled, quantitative analysis of receptor binding and membrane fusion kinetics in a native membrane context. As proof of concept, we reconstitute the SARS-CoV-1 Spike-ACE2 interaction, capturing specific receptor engagement and accumulation at the membrane interface using confocal microscopy and micropipette aspiration. Fusion was induced by proteolytic activation and quantified using both high-resolution microscopy and high-throughput Imaging Flow Cytometry. The platform also reveals the influence of membrane composition on fusion efficiency, demonstrated by the impact of cholesterol depletion. This approach provides a broadly applicable system for dissecting membrane fusion and protein-protein interactions across membranes, with compatibility for biophysical, imaging and structural analysis. It offers new opportunities for mechanistic studies and inhibitor screening in a biologically relevant yet experimentally accessible context.