[Perspective] Multisite phosphorylation by MAPK

Reversible protein phosphorylation plays a fundamental role in signal transduction networks. Phosphorylation alters protein function by regulating enzymatic activity, stability, cellular localization, or binding partners. Over three-quarters of human proteins may be phosphorylated, with many targeted at multiple sites. Such multisite phosphorylation substantially increases the scope for modulating protein function—a protein with n phosphorylation sites has the potential to exist in 2n distinct