Characterization of the endogenous mono-ADP-ribosylation stimulated by brefeldin A

We have recently described a novel enzymatic mono-ADP-ribosyl transfer reaction induced by brefeldin A, a well characterized inhibitor of vesicular traffic, which selectively modifies two cytosolic proteins of 38 kDa (p38) and 50 kDa (BARS-50). p38 was identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a glycolytic enzyme and a multifunctional protein involved in several cellular processes; BARS-50 might be a novel G protein, since it is able to bind GTP and the beta gamma subunit of G proteins. We have characterized this enzymatic activity and screened in vitro the effects of different drugs belonging to the coumarine (dicumarol, coumermicin A1 and novobiocin) and quinone (ilimaquinones, benzoquinones and naphtoquinones) class. These drugs blocked the BFA-dependent mono-ADP-ribosylation, showed remarkable effects on Golgi morphology in control cells, and antagonized the tubular reticular redistribution of the Golgi complex in brefeldin A treated cells (see papers of Corda and Colanzi in this issue) suggesting a possible role for ADP-ribosylation in both the cellular effects of brefeldin A and the maintenance of the structure/function of the Golgi complex.