Affinity methods for phosphorylation-dependent interactions.

14-3-3s are a highly conserved protein family that exert many regulatory roles in eukaryotic cells by binding to phosphopeptide motifs in diverse target proteins. Here, we describe 14-3-3 affinity binding procedures that can be used to purify and identify 14-3-3-binding phosphoproteins; monitor how their phosphorylation and 14-3-3 binding is regulated by extracellular stimuli; define the functional effects of 14-3-3s on individual targets; and identify relevant protein phosphatases and kinases. In principle, these methods could be adapted to characterize other types of protein-protein interaction that depend on covalent modification of target sites.