PEA‐15 Uses a Common Scaffold to Interact with Different Binding Partners in a Phosphorylation‐Dependent Manner

PEA‐15, phosphoprotein enriched in astrocytes, 15 kDa, performs a variety of functions in regulating cellular pathways, such as cell proliferation and apoptosis. The protein consists of a death effector domain (DED) and a long, irregular structured C‐terminal tail. We hypothesize that phosphorylation of the C‐terminal tail residues, Ser‐104 and Ser‐116, promotes conformational changes at the DED, and alters the binding specificity from extracellular regulated kinase‐2 (ERK2) to Fas associated death domain (FADD). To test the hypothesis, we used the molecular dynamics package, GROMACS, to simulate the complexes between unphosophorylated PEA‐15 and ERK2, and doubly phosphorylated PEA‐15 (PEA‐15pp) and FADD on a GPU‐equipped Linux workstation, with simulation time up to 150 ns. The simulated complex structures were analyzed and visualized with VMD and PyMOL programs. The computational experiments revealed that the DED conformations and surface polar interactions are dependent on phosphorylation states of the C‐terminal serine residues. The binding interfaces between PEA‐15 and ERK and PEA‐15pp and FADD are similarly composed of a scaffold that includes both DED and C‐terminal tail residues of PEA‐15. Residues from helices 5 and 6 of the DED directly interact with either ERK2 or FADD, while helices 2, 3, and 4 become more flexible in the complex structures than the free‐form protein. PEA‐15 also uses the same stretch of its irregular C‐terminal tail to interact with FADD or ERK2 (residues 116‐130). Phosphorylation of Ser‐104 and Ser‐116 on the C‐terminal tail alters the binding specificity from ERK2 to FADD, as the negatively charged phosphoryl groups interacts with positively charged amino acids on FADD, while there are no charge‐charge interactions of the C‐terminal tail with ERK2.