Abstracts (complete list) - Wissenschaft Online

Tobias Schwerd, Johannes C. Hellmuth, Andreas Schmidt, Hendrik Poeck, Michael
Wenzel, Stefan Endres, Simon Rothenfusser
Molecular mechanisms of virus recognition by Rig-I-like
helicases
Viral infections are a constant threat to the integrity of human beings. Survival of the
host organism depends on the rapid induction of innate immune responses including the
production of interferon type I. The newly described family of cytoplasmic Rig-I-like
helicases sense viral infection via the recognition of viral RNA, and trigger a potent
antiviral defense. This family comprises Retinoic acid-inducible gene I (RIG-I) and
melanoma differentiation associated gene 5 (MDA-5) two non-redundant signalling
receptors and the regulatory protein Lgp-2.Rig-I was recently shown to bind and detect
RNA of negative stranded RNA viruses, via a virus-specific 5’-triphosphate modification
absent in normal cytoplasmic RNAs. This provided a structural basis for the distinction
of self- and non-self RNA. We are interested in the molecular details leading from ligandbinding
by these helicases to the activation of anti-viral signalling processes.
Classically, helicases are known to unwind double-stranded (ds)RNA in an ATPdependent
fashion. Using an in vitro assay we demonstrate, that the ATPase activity of
RIG-I is triggered in the presence of dsRNA. Interestingly, RIG-I-dependent ATP
hydrolysis can also be activated by in vitro transcribed but not synthetic single-stranded
(ss)RNA. In both settings activation of RIG-I’s ATPase activity is independent of 5’-end
modifications. To investigate the correlation between helicase activity and signalling we
tested a similar set of ligands in IFN-beta luciferase reporter assays. Our experiments
indicated that helicase activity triggered by dsRNA is required but not sufficient for IFN
promoter activation. In addition, pull-down assays show that an intact ATP-binding
motif is not needed for ligand binding.
In conclusion, we propose that double-strandedness is an important molecular feature
for recognition and downstream signaling of viral RNA by Rig-I. This may facilitate the
development of new therapeutic molecules in tumor immunology and viral infection.