ECTO-ADP-RIBOSYLTRANSFERASE ACTIVITY OF PSEUDOMONAS-AERUGINOSA EXOENZYME-S

Pseudomonas aeruginosa produces two ADP-ribosyltransferases, exotoxin A and exoenzyme S (ExoS), Although the physiological target protein re mains to be defined, ExoS has been shown to ADP-ribosylate several euk aryotic proteins in vitro, including vimentin and members of the famil y of low-molecular-weight GTP-binding proteins, Recently, ExoS ADP-rib osyltransferase activity has been detected in the pleural fluid of rab bits infected with P. aeruginosa, This observation prompted an examina tion of the potential for ExoS to function as an ecto-ADP-ribosyltrans ferase. We have observed that ExoS preferentially ADP-ribosylated two extracellular serum proteins with molecular masses of 150 and 27 kDa, The ADP-ribosylation of these serum proteins by ExoS was stimulated by , but not dependent upon, exogenous FAS (for factor activating exoenzy me S), which indicated that serum contained endogenous FAS activity, B iochemical analysis showed that the 150-kDa GDP-ribosylated protein wa s immunoglobulin of the immunoglobulin G (IgG) and IgA classes. Subtyp ing showed that ExoS preferentially ADP-ribosylated human IgG3 and tha t ADP-ribosylation occurred within its Fc region, The 27-kDa protein A DP-ribosylated by ExoS was determined to be apolipoprotein Al, These d ata demonstrate ecto-ADP-ribosyltransferase activity by ExoS, This may extend the potential physiological consequences of ExoS during infect ion by P. aeruginosa beyond the implicated type III secretion-mediated intracellular delivery of ExoS into sensitive eukaryotic cells.