STUDIES ON THE ACTIVE-SITE STRUCTURE OF C3-LIKE EXOENZYMES - INVOLVEMENT OF GLUTAMIC-ACID IN CATALYSIS OF ADP-RIBOSYLATION

Various C3-like ADP-ribosyltransferases like Clostridium botulinum exo enzyme C3, C limosum transferase, B cereus transferase and a transfera se from Staphylococcus aureus (EDIN) selectively modify the low-molecu lar mass GTP-binding proteins RhoA,B,C. UV-irradiation of C linosum tr ansferase in the presence of [carbonyl-C-14]NAD resulted in radiolabel ing of Glu-174. Concomitantly, ADP-ribosyltransferase and NAD glycohyd rolase activities were inhibited. Site-directed mutagenesis of Glu-174 (E174D, E174Q) which resulted in more than 1000-fold reduction of enz yme activity, suggests that the glutamic acid residue is essentially i nvolved in the catalytic action of C3-like transferases. These finding s support the view that all bacterial ADP-ribosyltransferases share a similar active-site structure.