PEG: The Magic Bullet for Biophysical Analysis of Highly Aggregating Small Molecules in Aqueous Solutions

Biophysical research plays a crucial role in drug discovery,butmany druglike molecules are poorly soluble and prone to aggregation,making their analysis challenging and susceptible to artifacts. Toaddress this issue, we propose an approach that uses poly(ethyleneglycol) (PEG) as an excipient in aqueous buffers to reduce the propensityof small molecules to aggregate. We show how PEG allows us to measurethe thermodynamics of a complex formed by a heterobifunctional SmallMolecule (hSM) that brings two proteins together. Our model accountsfor all of the equilibrium states of the small molecule in solution,resulting in more precise parameters for describing how the proteinsand the ligand interact. These precise parameters are important fordesigning better lead molecules.