The function of proteins, and their malfunction in disease, is governed by their interactions with each themselves and with other biomolecules. Mass photometry provides a new and uniquely powerful means to quantify these interactions in terms of physically meaningful quantities, such as dissociation constants and free energies. This opens the door for measuring the manipulation of these interactions in drug development.
Complex protein-protein interactions can be quantified by mass photometry. The Env glycoprotein of the HIV virus is targeted by antiviral lectins which either bind to single Envs or cross-links Env units. At low concentration of lectin, the Env is primarily a single unit. At higher lectin concentration, higher order Env units are detected, and found to include bound lectins. From the titration curve and relative amounts of Env-lectin complexes, the associated binding of each interaction can be quantified providing key information for understanding anti-viral mechanisms.