ID: 145: Theiler’s virus L∗ protein inhibits RNase L dimerization and activation by binding to the 2-5A-binding pocket of the enzyme
We observed previously that the L ∗ protein of Theiler’s virus (picornavirus) inhibited RNase L, through direct protein–protein interaction. Interestingly, RNase L inhibition by L ∗ exhibits species-specificity as L ∗ inhibits mouse but not human RNase L [1] . We took advantage of this species specificity to map the L ∗ binding site on RNase L, by testing L ∗ -mediated inhibition of a series of human-mouse RNase L chimeras. Our results suggest that L ∗ interacts at two sites within RNase L ankyrin repeats 1 and 2. According to the recently solved structure of dimeric RNase L [2] , [3] , our results are compatible with RNase L inhibition through both dimerization and 2-5A-binding antagonism. We therefore established a crosslinking-based RNase L dimerization assay and show that L ∗ indeed inhibits RNase L dimerization. Next, we analyzed whether L ∗ could interfere with 2-5A binding. Competitive binding studies by surface plasmon resonance demonstrated that L ∗ indeed competes with 2-5A binding to mouse but not human RNase L. In conclusion, protein L ∗ of Theiler’s virus inhibits the OAS/RNase L pathway by binding to RNase L ankyrin repeats 1 and 2, thereby preventing 2-5A-mediated dimerization and activation of RNase L. L ∗ is the first viral protein we know of that antagonizes the OAS/RNase L pathway by acting on the effector enzyme.