Phosphoprotein enriched in astrocytes, 15 kDa (PEA-15) exerts its regulatory roles on several critical cellular pathways through protein–protein interactions depending on its phosphorylation states. It can either inhibit the extracellular signal-regulated kinase (ERK) activities when it is dephosphorylated or block the assembly of death-inducing signaling complex (DISC) and the subsequent activation of apoptotic initiator, caspase-8, when it is phosphorylated. Due to the important roles of PEA-15 in regulating these pathways that lead to opposite cellular outcomes (cell proliferation vs. cell death), we proposed a phosphostasis (phosphorylation homeostasis) model, in which the phosphorylation states of the protein are vigorously controlled and regulated to maintain a delicate balance. The phosphostasis gives rise to the protective cellular functions of PEA-15 to preserve optimum cellular conditions. In this article, using advanced multidimensional nuclear magnetic resonance (NMR) techniques combined with a novel chemical shift (CS)-Rosetta algorithm for de novo protein structural determination, we report a novel conformation of PEA-15 death-effector domain (DED) upon interacting with ERK2. This new conformation is modulated by the irregularly structured C-terminal tail when it first recognizes and binds to ERK2 at the d-peptide recruitment site (DRS) in an allosteric manner, and is facilitated by the rearrangement of the surface electrostatic and hydrogen-bonding interactions on the DED. In this ERK2-bound conformation, three of the six helices (α2, α3, and α4) comprising the DED reorient substantially in comparison to the free-form structure, exposing key residues on the other three helices that directly interact with ERK2 at the DEF-docking site (docking site for ERK, FxF) and the activation loop. Additionally, we provide evidence that the phosphorylation of the C-terminal tail leads to a distinct conformation of DED, allowing efficient interactions with Fas-associated death domain (FADD) protein at the DISC. Our results substantiate the allosteric regulatory roles of the C-terminal tail in modulating DED conformation and facilitating protein–protein interactions of PEA-15.

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Trans‐activator of transcription, TAT, one of the proteins that is expressed by the HIV genome, has been heavily associated with HIV‐associated cognitive morbidities. In vitro experiments have shown that the presence of TAT disrupts blood‐brain barrier (BBB) tight junctions and overall integrity. The mechanisms for TAT associated BBB disruption remain largely unknown.Phosphoprotein enriched in astrocytes (PEA‐15) is a ubiquitously expressed protein that is best known for its ability to regulate critical cellular pathways via protein‐protein interactions. PEA‐15 gains multiple protein binding affinities depending on the phosphorylation states of its residues Ser104 and Ser116. When PEA‐15 is phosphorylated at both Ser104 and Ser116 it gains high affinity to the Fas‐associated death domain (FADD). When protein‐protein binding with FADD, PEA‐15 blocks FADD from inducing apoptosis by preventing it from activating Caspase‐8.By blocking FADD effector functions via transfecting a phosphomimetic mutant of PEA‐15, in which both Ser104 and Ser116 are replaced with Aspartic Acid (PEA‐15‐DD), into primary human brain microvascular endothelial cells, we set to explore the mechanisms of HIV‐TAT mediated disruption of BBB tight junctions.Support or Funding InformationThis research is supported by NIH Grant R21DA046223This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.