Monitoring Disassembly and Cargo Release of Phase-Separated Peptide Coacervates with Native Mass Spectrometry

[Image: see text] Engineering liquid–liquid phase separation (LLPS) of proteins and peptides holds great promise for the development of therapeutic carriers with intracellular delivery capability but requires accurate determination of their assembly properties in vitro, usually with fluorescently labeled cargo. Here, we use mass spectrometry (MS) to investigate redox-sensitive coacervate microdroplets (the dense phase formed during LLPS) assembled from a short His- and Tyr-rich peptide. We can monitor the enrichment of a reduced peptide in dilute phase as the microdroplets dissolve triggered by their redox-sensitive side chain, thus providing a quantitative readout for disassembly. Furthermore, MS can detect the release of a short peptide from coacervates under reducing conditions. In summary, with MS, we can monitor the disassembly and cargo release of engineered coacervates used as therapeutic carriers without the need for additional labels.