How bacterial ADP-ribosylating toxins recognize substrates |
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Authors: | Sun Jianjun Maresso Anthony W Kim Jung-Ja P Barbieri Joseph T |
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Institution: | Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, USA. |
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Abstract: | ExoS and ExoT are bifunctional type III cytotoxins of Pseudomonas aeruginosa that contain an N-terminal RhoGAP domain and a C-terminal ADP-ribosylation domain. Although they share 76% amino acid identity, ExoS and ExoT ADP-ribosylate different substrates. Using protein modeling and site-directed mutagenesis, the regions of ExoS and ExoT that define substrate specificity were determined. Regions B (active site loop), C (ARTT motif) and E (PN loop) on ExoS are necessary and sufficient to recognize ExoS targets, whereas regions B, C and E on ExoT are necessary but not sufficient to recognize ExoT targets, such as the Crk proteins. A specific Crk recognition motif on ExoT was defined as region A (helix alpha1). The electrostatic properties of regions A, B, C and E define the substrate specificity of ExoS and ExoT and these interactions can explain how other bacterial ADP-ribosylating toxins recognize their unique substrates. |
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