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.