14-3-3 proteins activate Pseudomonas exotoxins-S and –T by chaperoning a hydrophobic surface

Tobias Karlberg, Peter Hornyak, Ana Filipa Pinto, Stefina Milanova, Mahsa Ebrahimi, Mikael Lindberg, Nikolai Püllen, Axel Nordström, Elinor Löverli, Rémi Caraballo, Emily V. Wong, Katja Näreoja, Ann-Gerd Thorsell, Mikael Elofsson, Enrique M. De La Cruz, Camilla Björkegren and Herwig Schüler

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Received: 8th June 18

Pseudomonas are a common cause of hospital acquired infections that may be lethal. ADP-ribosyltransferase activities of Pseudomonas exotoxin-S and -T depend on 14-3-3 proteins inside the host cell. By binding in the 14-3-3 phosphopeptide binding groove, a hydrophobic C-terminal helix of ExoS and ExoT has been thought to be crucial for their activation. However, crystal structures of the 14-3-3β:ExoS and -ExoT complexes presented here reveal an extensive novel binding interface that is sufficient for complex formation and toxin activation. We show that C-terminally truncated ExoS ADP-ribosyltransferase domain lacking the hydrophobic binding motif is active when co-expressed with 14-3-3. Moreover, swapping the hydrophobic C-terminus with a fragment from Vibrio Vis toxin creates a 14-3-3 independent toxin that ADP-ribosylates known ExoS targets. Finally, we show that 14-3-3 stabilizes ExoS against thermal aggregation. Together, this indicates that 14-3-3 proteins activate exotoxin ADP-ribosyltransferase domains by chaperoning their hydrophobic surfaces independently of the hydrophobic C-terminal segment.

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This is an abstract of a preprint hosted on an independent third party site. It has not been peer reviewed but is currently under consideration at Nature Communications.

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