Mass-specific single molecule pull-down from complex mixtures with bilayer-assisted mass photometry

Abstract Determining the identity, quantity and interactions of proteins is fundamental to studies of biomolecular function and (dis)regulation in disease. Here, we combine mass photometry with supported lipid bilayers (SLBs) to specifically recruit proteins of interest from complex mixtures such as cell lysate and demonstrate sensitive detection and mass measurement of single biomolecules and their complexes without prior purification. Extending to heterologously expressed proteins, we provide rapid information on oligomerisation and concentration in lysate. Introduction of polyethylene glycol in the SLBs passivates against a variety of cell lysates and serum, allows specific recruitment of proteins from complex mixtures and mass-specific detection and affinity measurement at sub-nM concentrations. Our approach preserves the mass resolution and accuracy of mass photometry, thereby enabling visualisation and quantification of oligomeric states, interactions and complexes directly from cell lysates.