ADP-ribosylation reactions in Sulfolobus solfataricus,a thermoacidophilic archaeon

An ADP-ribosylating system was detected in a crude homogenate from Sulfolobus solfataricus, a thermophilic archaeon, optimally growing at 87°C. The archaeal ADP-ribosylation reaction was time-, temperature- and NAD-dependent. It proved to be highly thermostable, with about 30% decrease of ¹⁴C incorporation from [¹⁴C]NAD on incubation at 80°C for up to 24 h. The main reaction product was found to be mono-ADP-ribose. Testing both [adenine- ¹⁴C(U)]NAD and [adenine- ¹⁴C(U)]ADPR as substrates, it was found that acceptor proteins were modified by ADP-ribose both enzymatically, via ADP-ribosylating enzymes, and via chemical attachment of free ADP-ribose, likely produced by NAD glycohydrolase activity. The synthesis of ADP-ribose-protein complexes was shown to involve mainly acceptors with molecular masses in the 40–100 kDa range, as determined by electrophoresis on polyacrylamide gel in the presence of sodium dodecyl sulphate.