Dissection of the roles of adenine ring nitrogen (N-1) and exocyclic amino (N-6) moieties in the interaction of 2-5A with RNase L.

To elucidate further the roles played by the adenine bases in the interaction of RNase L (EC 3.1.2.6) with the 2',5'-oligoadenylate 2-5A, p5'A2'(p5'A2')np5' A, a series of sequence-specific 1-deazaadenosine (c1A)-substituted analogues were synthesized and evaluated for their ability to bind to and activate human RNase L in comparison to earlier reported inosine-substituted congeners of 2-5A. Substitution of only the 5'-terminal adenosine of p5'A2'p5'A2 p5 A with c1A afforded an analogue with strongly diminished RNase L binding and activation ability, while replacement of the second or middle adenosine of p5 A2' p5'A2'p5' A had only a modest effect. In distinct contrast to p5'A2'p5'A2'p5'I, the c1A analogue with the third or 2'-terminal adenosine replacement approached parent p5' A2'p5'A2'p5' A in RNase L activation ability. These results permitted a further dissection of the role of various nucleotidic functional groups in the interaction of 2-5A with RNase L: specifically, that the 5'-terminal adenosine purine N-1 moiety is key for binding to RNase L, while the 2'-terminal adenosine N-6 exocyclic amino group is critical for RNase L activation.