Pseudomonas aeruginosa ExoT ADP-ribosylates CT10 regulator of kinase (Crk) proteins.

Pseudomonas aeruginosa ExoT is a type III cytotoxin that functions as an anti-internalization factor with an N-terminal RhoGAP domain and a C-terminal ADP-ribosyltransferase domain. Although ExoT RhoGAP stimulates actin reorganization through the inactivation of Rho, Rac, and Cdc42, the function of the ADP-ribosylation domain is unknown. The present study characterized the mammalian proteins that are ADP-ribosylated by ExoT, using two-dimensional SDS-PAGE and matrix-assisted laser desorption ionization/time of flight (MALDI-TOF) analysis. ExoT ADP-ribosylated two cytosolic proteins in cell lysates upon type III delivery into cultured HeLa cells. MALDI-TOF mass spectrometry analysis identified the two proteins as Crk-I and Crk-II that are Src homology 2-3 domains containing adaptor proteins, which mediate signal pathways involving focal adhesion and phagocytosis. ExoT ADP-ribosylated recombinant Crk-I at a rate similar to the ADP-ribosylation of soybean trypsin inhibitor by ExoS. ExoS did not ADP-ribosylate Crk-I. ADP-ribosylation of Crk-I may be responsible for the anti-phagocytosis phenotype elicited by ExoT in mammalian cells.