title: Glucosylation and ADP ribosylation of rho proteins: effects on nucleotide binding, GTPase activity, and effector coupling.
abstract: We studied the effects of glucosylation of RhoA, Rac1, and Cdc42 at threonine-35 and -37 by Clostridium difficile toxin B on nucleotide binding, GTPase activity, and effector coupling and compared these results with the ADP ribosylation of RhoA at asparagine-41 catalyzed by Clostridium botulinum C3 transferase. Whereas glucosylation and ADP ribosylation had no major effects on GDP release from RhoA, Rac1, and Cdc42, the rate of GTPgammaS release from Rho proteins was increased 3-6-fold by glucosylation. ADP ribosylation decreased the rate of GTPgammaS release by about 50%. Glucosylation reduced the intrinsic activities of the GTPases by 3-7-fold and completely blocked GTPase stimulation by Rho-GAP. In contrast, ADP ribosylation slightly increased GTPase activity ( approximately 2-fold) and had no major effect on GAP stimulation of GTPase. Whereas ADP ribosylation did not affect the interaction of RhoA with the binding domain of protein kinase N, glucosylation inhibited this interaction. Glucosylation of Rac1 markedly diminished its ability to support the activation of the superoxide-generating NADPH oxidase of phagocytes. Glucosylated Rac1 did not interfere with NADPH oxidase activation by unmodified Rac1, even when present in marked molar excess, indicating that it was incapable of competing for a common effector. The data indicate that the functional inactivation of small GTPases by glucosylation is mainly caused by inhibition of GTPase-effector protein interaction.
authors.affiliation: Institut für Pharmakologie und Toxikologie der Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Strasse 5, D-79104 Freiburg, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Sehr
authors.forename: G
authors.initials: G
authors.lastname: Joseph
authors.forename: H
authors.initials: H
authors.lastname: Genth
authors.forename: I
authors.initials: I
authors.lastname: Just
authors.forename: E
authors.initials: E
authors.lastname: Pick
authors.forename: K
authors.initials: K
authors.lastname: Aktories
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D001426:Bacterial Proteins; D001427:Bacterial Toxins / Q000378:metabolism; D001905:Botulinum Toxins; D018797:Cell Cycle Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D019255:NADPH Oxidases / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D018797:Cell Cycle Proteins; D006023:Glycoproteins; C031815:toxB protein, Clostridium difficile; D006153:Guanosine Diphosphate; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D019255:NADPH Oxidases; D005964:Glucosyltransferases; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D005947:Glucose