The 52 kDa Adp-Ribosylated Protein in the Rat Heart Plasma Membrane: Is It G_sa?

Abstract

G proteins¹ are a family of heterotrimeric molecules that are implicated in a variety of signal transduction processes (for review see 1). ADP-ribosylation is a covalent modification which transfers the ADP-ribose moiety of NAD to cellular acceptor proteins. Several bacterial toxins posses this ADP-ribosyltransferase activity and modify several G proteins. For example, cholera toxin can ADP-ribosylate the α subunits of the G proteins G_s and transducin (1). These toxins may mimic endogenous processes and G proteins may be endogenously ADP-ribosylated. Indeed several authors have demonstrated that G_sα can be ADP-ribosylated by endogenous ADP-ribosyltransferases (2-6). In liver membranes, a 55 kDa protein which was speculated to be G_sα is ADP-ribosylated in both the absence and presence of cholera toxin. In the presence of isoproterenol ADP-ribosylation of this protein is increased (6). In NG108-15 hybrid cells (5) and in platelets (4) ADP-ribosylation of G_sα has been implicated in heterologous desensitization to prostacyclins. Recently, it was also shown that in canine sarcolemma, adenylyl cyclase might be regulated by endogenous, reversible ADP-ribosylation of G_sα (7).

Article Footnote

G proteins, guanine nucleotide binding proteins; G_sα , alpha subunit of the stimulatory guanine nucleotide binding protein.