69-kDa and 100-kDa isoforms of interferon-induced (2'-5')oligoadenylate synthetase exhibit differential catalytic parameters.
The (2'-5')oligoadenylate synthetase represents a family of interferon-induced proteins which when activated by double-stranded (ds)RNA polymerizes ATP into 2'-5'-linked oligomers with the general formula pppA(2'p5'A)n, where n > 1, which for convenience are referred to as 2-5A. We studied here the influence of pH, dsRNA concentration and time on oligomeric composition of 2-5A synthesized by purified 69-kDa and 100-kDa isoforms of (2'-5')oligo(adenylate) synthetase. In optimal conditions for activity, the 69-kDa form synthesized higher oligomers of 2-5A molecules whereas the 100 kDa form synthesized preferentially dimeric molecules, which are known not to be functional for the activation of RNase L. This difference does not reflect a differential affinity of the enzymes for the preformed 2-5A dimer, which is found to be a very poor substrate for both enzymes. This latter strongly suggests that the mechanism of elongation is more likely processive. Moreover, we show that both isoforms have efficient nucleotidyl-transferase activity and provide evidence that, in optimized conditions, GTP can be used alone as substrate by these enzymes to generate pppG2'p5'G. Our results clearly demonstrate that the 69-kDa and 100-kDa forms of (2'-5')oligoadenylate synthetase manifest various differential catalytic activities, and favor the hypothesis that these enzymes might have other functions in the cell besides those in the 2-5A system.
Marié
I
I
Unité de Virologie et Immunologie Cellulaire (ERS CNRS 572) Institut Pasteur, Paris, France.
Blanco
J
J
Rebouillat
D
D
Hovanessian
A G
AG
D015088:2',5'-Oligoadenylate Synthetase / Q000187:drug effects / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007372:Interferons / Q000494:pharmacology*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D013379:Substrate Specificity
D007527:Isoenzymes; D006160:Guanosine Triphosphate; D007372:Interferons; D015088:2',5'-Oligoadenylate Synthetase