title: 14-3-3 proteins are required for the inhibition of Ras by exoenzyme S.
abstract: 14-3-3 proteins play a regulatory role and participate in both signal transduction and checkpoint control pathways. 14-3-3 proteins bind phosphoserine ligands, such as Raf-1 kinase and Bad, by recognizing the phosphorylated consensus motif, Arg-Ser-Xaa-pSer-Xaa-Pro (where 'Xaa' represents 'any residue', and 'pSer' is 'phosphoserine'). However, 14-3-3 proteins must bind unphosphorylated ligands, such as glycoprotein Ibalpha and Pseudomonas aeruginosa exoenzyme S (ExoS), since it has been suggested that specific residues of 14-3-3 proteins are required for activation of ExoS. Furthermore, an unphosphorylated peptide derived from a phage display library inhibited the binding of both ExoS and Raf-1 to 14-3-3, and bound within the same conserved amphipathic groove on the surface of 14-3-3 as the Raf-derived phosphopeptide (pS-Raf-259). In the present study we identify the interaction site on ExoS for 14-3-3, and show that ExoS and 14-3-3 do indeed interact in vivo. In addition, we show that this interaction is critical for the ADP-ribosylation of Ras by ExoS, both in vitro and in vivo. Loss of the 14-3-3 binding site on ExoS results in an ExoS molecule that is unable to efficiently inactivate Ras, and displays reduced killing activity.
authors.affiliation: Cellular and Molecular Biology, University of Umeâ, S-901 87 Umeâ, Sweden.
authors.forename: M L
authors.initials: ML
authors.lastname: Henriksson
authors.forename: U
authors.initials: U
authors.lastname: Trollér
authors.forename: B
authors.initials: B
authors.lastname: Hallberg
mesh_terms: D048948:14-3-3 Proteins; D016475:3T3 Cells; D036002:ADP Ribose Transferases / Q000378:metabolism*; D000818:Animals; D001427:Bacterial Toxins; D001665:Binding Sites; D006367:HeLa Cells; D006801:Humans; D020014:K562 Cells; D051379:Mice; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism / Q000502:physiology*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D048948:14-3-3 Proteins; D001427:Bacterial Toxins; D014446:Tyrosine 3-Monooxygenase; D036002:ADP Ribose Transferases; C444820:exoenzyme S; D018631:ras Proteins