Elucidating the Stoichiometries of Host-Pathogen Protein Interactions with Mass Photometry.

Mass photometry (MP) is a single molecule technique that enables the characterization of individual proteins. Here we show a detailed workflow using the Refeyn One to investigate molecular complexes, using the M53 protein, a plasminogen-binding group A streptococcal M-like protein (PAM), and human plasminogen as exemplar proteins. The methodology described herein confirmed a 1:1 binding stoichiometry for the M53-plasminogen complex. Additionally, MP was used to identify the oligomerization state, homogeneity, purity, and approximate molecular weights of each protein.