TOXIN-INDUCED ACTIVATION OF THE G-PROTEIN P21-RHO BY DEAMIDATION OF GLUTAMINE

Pathogenic Escherichia coli are responsible for a variety of diseases, including diarrhoea, haemolytic uraemic syndrome, kidney infection, s epticaemia, pneumonia and meningitis. Toxins called cytotoxic necrotiz ing factors (CNFs) are among the virulence factors produced by uropath ogenic (CNF1)(1) or enteropathogenic (CNF2)(2) E. coli strains that ca use diseases in humans and animals, respectively. CNFs induce an incre ase in the content of actin stress fibres and focal contacts in cultur ed cells(3,4). Effects of CNFs on the actin cytoskeleton correlated wi th a decrease in the electrophoretic mobility of the GTP-binding prote in Rho(4,5) and indirect evidence indicates that CNF1 might constituti vely activate Rho(6). Here we show that CNF1 catalyses the deamidation of a glutamine residue at position 63 of Rho, turning it into glutami c acid, which inhibits both intrinsic GTP hydrolysis and that stimulat ed by its GTPase-activating protein (GAP). Thus, this deamidation of g lutamine 63 by CNF1 leads to the constitutive activation of Rho, and i nduces the reorganization of actin stress fibres. To our knowledge, CN F1 is the first example of a bacterial toxin acting by deamidation of a specific target protein.