CHARACTERIZATION OF MAMMALIAN ADP-RIBOSYLATION CYCLES

NAD:arginine ADP-ribosyltransferases catalyze the transfer of the ADP- ribose moiety from NAD to an arginine in an acceptor protein, whereas ADP-ribosylarginine hydrolases remove ADP-ribose, regenerating free ar ginine and completing an ADP-ribosylation cycle. A family of four mono -ADP-ribosyltransferases was isolated and characterized from turkey er ythrocytes. Transferases from rabbit and human skeletal muscle were cl oned. The muscle transferases are glycosylphosphatidylinositol-anchore d proteins and highly conserved across mammalian species. The rat T ce ll alloantigen RT6.2 has significant amino acid sequence identity to t he muscle ADP-ribosyltransferase. Mammalian cells transformed with the RT6.2 coding region cDNA expressed NAD glycohydrolase activity. Seque nces of RT6.2, rabbit muscle transferase and several of the bacterial toxin ADP-ribosyltransferases contain regions of amino acid similarity which, in the bacterial toxin ADP-ribosyltransferases, form the NAD-b inding and active-site domains. ADP-ribosylarginine hydrolase, initial ly purified from turkey erythrocytes, was cloned from rat, mouse, and human brain. Deduced amino acid sequences of the rat and mouse hydrola ses were 94% identical with five conserved cysteines whereas the human hydrolase sequence was 83% identical to that of the rat, with four co nserved cysteines. It is unclear how an intracellular hydrolase acts i n concert with a surface ADP-ribosyltransferase.