Exoenzyme S binds its cofactor 14-3-3 through a non-phosphorylated motif.
14-3-3 proteins belong to a family of conserved molecules, which play a regulatory role and participate in signal transduction and checkpoint control pathways. 14-3-3 proteins bind phosphoserine-phosphorylated ligands, such as the Raf-1 kinase and Bad, through recognition of the phosphorylated consensus motif, RSXpSXP (where pS is phosphoserine). Recently, a phosphorylation-independent interaction has been reported to occur between 14-3-3 and a small number of proteins, for example the 43 kDa inositol polyphosphate 5-phosphatase, glycoprotein Ib, p75NTR-associated cell-death executor (NADE) and the bacterial ADP-ribosyltransferase toxin exoenzyme S (ExoS). It has been suggested that specific residues of 14-3-3 proteins are required for activation of the bacterial toxin ExoS. An unphosphorylated peptide derived from a phage display library, known as the R18 peptide, and a synthetic peptide derived from ExoS inhibit the interaction between ExoS and 14-3-3. In this report we identify the amino acid sequence on ExoS which is responsible for its specific interaction with 14-3-3, both in vitro and in vivo. In addition, we believe that this interaction is critical for the ADP-ribosylation of an endogenous target, 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 shows a reduced capacity to change the morphology of infected cells, together with reduced killing activity.
Department of Medical Biosciences/Pathology, Umeå University, S-901 87 Umeå, Sweden. Bengt.Hallberg@cmb.umu.se
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D048948:14-3-3 Proteins; D036002:ADP Ribose Transferases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D001665:Binding Sites; D016384:Consensus Sequence; D003603:Cytotoxins / Q000378:metabolism; D006801:Humans; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D048948:14-3-3 Proteins; D001427:Bacterial Toxins; D003603:Cytotoxins; D010750:Phosphoproteins; D014446:Tyrosine 3-Monooxygenase; D036002:ADP Ribose Transferases; C444820:exoenzyme S