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14-3-3 proteins belong to a family of conserved molecules expressed in all eukaryotic cells, which play an important role in a multitude of signaling pathways. 14-3-3 proteins bind to phosphoserine⁄phosphothreonine motifs in a sequence-specific manner. More than 200 14-3-3 binding partners have been found that are involved in cell cycle regulation, apoptosis, stress responses, cell metabolism and malignant transformation. | iFEBS Journal Delineation of exoenzyme S residues that mediate the interaction with 14-3-3 and its biological activity Lubna Yasmin1 Anna L. Jansson1 z Tooba Panahandeh1 Ruth H. Palmer3 Matthew S. Francis2 and Bengt Hallberg1 1 Department of Medical Biosciences Pathology Umea University Sweden 2 Department of Molecular Biology Umea University Sweden 3 Umea Center for Molecular Pathogenesis Umea University Sweden Keywords ADP-ribosylation coenzyme binding site cytotoxicity NAD-dependent cystic fibrosis Pseudomonas aeruginosa Correspondence B. Hallberg Department of Medical Biosciences Pathology Building 6m 2nd floor Umea University 901 87 Umea Sweden Fax 46 90 785 2829 Tel 46 90 785 2523 E-mail Bengt.Hallberg@medbio.umu.se Both authors contributed equally to this work. Received 5 October 2005 revised 7 December 2005 accepted 12 December 2005 14-3-3 proteins belong to a family of conserved molecules expressed in all eukaryotic cells which play an important role in a multitude of signaling pathways. 14-3-3 proteins bind to phosphoserine phosphothreonine motifs in a sequence-specific manner. More than 200 14-3-3 binding partners have been found that are involved in cell cycle regulation apoptosis stress responses cell metabolism and malignant transformation. A phosphorylation-independent interaction has been reported to occur between 14-3-3 and a C-terminal domain within exoenzyme S ExoS a bacterial ADP-ribosyltransferase toxin from Pseudomonas aeruginosa. In this study we have investigated the effect of amino acid mutations in this C-terminal domain of ExoS on ADP-ribosyltransferase activity and the 14-3-3 interaction. Our results suggest that leucine-428 of ExoS is the most critical residue for ExoS enzymatic activity as cytotoxicity analysis reveals that substitution of this leucine significantly weakens the ability of ExoS to mediate cell death. Leucine-428 is also required for the ability of ExoS to modify the eukaryotic endogenous target Ras. Finally single amino
