IDENTIFICATION OF GANGLIOSIDES AS INHIBITORS OF ADP-RIBOSYLTRANSFERASES OF PERTUSSIS TOXIN AND EXOENZYME C3 FROM CLOSTRIDIUM-BOTULINUM

We have previously reported the presence of an endogenous inhibitory activity in bovine brain for the ADP-ribosylation of GTP-binding proteins catalyzed by pertussis toxin (PT) (Hara-Yokoyama, M., and Furuyama, S, (1989) Biochem. Biophys. Res. Commun. 160, 67-71). In the present study, we identified the inhibitor as a ganglioside, The screening of various gangliosides revealed that G(Q1b alpha) most effectively inhibited the ADP-ribosyltransferase activities of both the holoenzyme and the catalytic subunit of PT. G(Q1b alpha) is a ganglioside newly identified as one of the antigens recognized by the cholinergic neuron-specific antibody, anti-Chol-1 alpha (Hirabayashi, Y,, Nakao, T,, Irie, F,, Whittaker, V,P., Ken, R,, and Ando, S. (1992) J. Biol. Chem. 267, 12973-12978), G(Q1b alpha) also inhibited the PT-catalyzed NAD(+) glycohydrolysis. Unlike PT activity, the ADP-ribosylation and the NAD(+) glycohydrolysis catalyzed by the C3 exoenzyme from Clostridium botulinum type C were inhibited by G(T1b) and G(Q1b). The ADP-ribosylation catalyzed by either PT or the C3 exoenzyme was not inhibited by ceramide, galactocerebroside, or sialic acid. In addition to the inhibitory action of gangliosides on ADP-ribosylation, the importance of gangliosides as regulators of NAD(+) metabolism is discussed.