A novel endoribonuclease from the marine sponge Tethya aurantium specific to 2',5'-phosphodiester bonds.

In the marine sponge Tethya aurantium a novel endoribonuclease was found which specifically catalyzed the degradation of 2',5'-phosphodiester linkages and was therefore named endo-2',5'-ribonuclease. This enzymatic reaction yielded 2',3'-cyclic phosphate and 5'-OH products similarly to the 3'-5' bond cleavage in RNA, catalyzed by metal-independent ribonucleases. The partially purified enzyme preparation was used for its biochemical characterization. The enzyme did not require the presence of metal ions for its activity. The novel nuclease exhibited a preference for 5'-phosphorylated 2',5'-oligoadenylates, but 2'-5' linkage in 5'-triphosphorylated hetero-oligomers or homo-dimers comprising guanylate or uridylate residues instead of adenylate was cleaved as well. The enzyme was also able to catalyze the degradation of 5'-unphosphorylated 2',5'-oligoadenylates, except for 2',5'-diadenylate, which were weaker substrates for the enzyme than the respective 5'-triphosphorylated forms. The observed substrate specificity may refer to the specific role of the enzyme in the degradation of natural 2',5'-oligoadenylates (2-5A) that function in the interferon-induced mammalian 2-5A system as allosteric regulators of ribonuclease L. They are produced by 2-5A synthetases (OAS) that are also present in sponges, the most ancient phylum of Metazoa. We suggest that the newly discovered endoribonuclease found in the marine sponge T. aurantium could be a representative of the group of 2',5'-specific ribonucleases that primarily control the cellular levels of 2',5'-oligoadenylates.