Quantifying ERK2-protein interactions by fluorescence anisotropy: PEA-15 inhibits ERK2 by blocking the binding of DEJL domains

While mitogen-activated protein kinase signaling pathways constitute highly regulated networks of protein-protein interactions, little quantitative information for these interactions is available. Here we highlight recent fluorescence anisotropy binding studies that focus on the interactions of ERK1 and ERY2 with PEA-15 (antiapoptotic phosphoprotein enriched in astrocytes-15 kDa), a small protein that sequesters ERK2 in the cytoplasm. The regulation of ERK2 by PEA-15 is appraised in the light of a simple equilibrium-binding model for reversible ERK2 nucleoplasmic-cytoplasmic shuttling, which elaborates on the theory of Burack and Shaw (J. Biol. Chem. 280, 3832-3837; 2005). Also highlighted is the recent observation that the peptide N-QKGKPRDLELPLSPSL-C, derived from the docking site for ERK/JNK and LEL (DEJL) in Elk- 1, displaces PEA- 15 from ERK2. It is proposed that the C-terminus of PEA-15 ((LXLXXXXKK129)-L-121) is a reverse DEJL domain [which has a general consensus of R/K Phi(A)-X-3/4-Phi(B), where Phi A and Phi B are hydrophobic residues (Leu, Ile, or Val)], which mediates one arm of a bidentate PEA-15 interaction with ERK2, The notion that PEA-15 is a potent inhibitor of many ERK2-mediated phosphorylations, by virtue of its ability to block ERK2-DEJL domain interactions, is proposed. (c) 2005 Elsevier B.V. All rights reserved.