Estimating the affinity of protein-ligand complex from changes to the charge-state distribution of a protein in electrospray ionization mass spectrometry

► New mass-spec related method for measuring weak protein-ligand interactions. ► Dissociation of a protein-ligand complex leads to charge-state shifts in a mass spectrum. ► The charge-state shift is correlated to the fraction of protein bound to ligand in solution. ► Apparent Kd values correlate well with those from other biophysical methods.