Mass Photometry Analysis of Membrane Proteins in Detergent Micelles

Mass photometry is a label-free technique that enables precise mass measurement of biomolecules in solution. It is a technique based on light scattering at the single-particle level: the scattering amplitude of biomolecules is directly proportional to their volume. Mass photometry has a very low protein concentration requirement, which is beneficial for work with proteins that are expressed in low yield or that require expensive purification protocols. The assays are fast and simple, which makes this technique increasingly valuable in structural biology workflows for characterization of particle distribution and size. In this chapter, we provide a step-by-step approach to use mass photometry, with a particular focus on its application for the analysis of membrane proteins in detergent micelles. We present a modification of the basic mass photometry workflow that enables the analysis of membrane proteins in the presence of detergents, which are essential for maintaining the stability of these proteins in solution but often introduce significant artifacts and noise. We discuss practical, accessible strategies to optimize the experimental conditions and show specific examples of their application to obtain high-quality measurements.