ADP-riboxanase effector that mediates arginine ADP-riboxanation of host target protein(s) (PubMed:34671164). Inhibits host CASP8 and apoptotic host cell death, possibly by catalyzing its ADP-riboxanation (PubMed:32657447). Does not catalyze ADP-riboxanation of host CASP4/CASP11 (PubMed:34671164). L-arginyl-[protein] + NAD(+) = ADP-riboxanated L-argininyl-[protein] + H(+) + NH4(+) + nicotinamide Secreted via the type III secretion system (TTSS). Host cells display apoptosis caused by strongly increased CASP8 activation. Belongs to the OspC family.