"We knew that the CARD domain was responsible for transmitting the antiviral signaling," Myong said. "And we knew how the 5'-triphosphate tag is detected. But a big question remained about the ATPase domain: It was using ATP to do something but what?"
To solve that mystery, the researchers used a technique termed "protein-induced fluorescent enhancement." This method makes use of a fluorescent dye that, when attached to a specific region of a molecule such as RNA, glows with more or less intensity depending on its proximity to a protein that is interacting with that molecule.
Using this technique, the researchers found that the RIG-I protein moves back and forth (translocates) selectively on double-stranded RNA, and that this activity is greatly stimulated in the presence of 5'-triphosphate.
By requiring both the 5'-triphosphate and the double-stranded RNA for it to function, the RIG-I protein is able to very accurately detect a viral invader, said Ha.
Most cellular RNAs have their triphosphate tails bobbed, capped or otherwise modified before circulating in the cytosol of the cell, he said. "So this is one powerful way of distinguishing viral RNA from cellular RNA."
Prior to this study, researchers did not know if RIG-I sensed both the double-stranded RNA and the 5'-triphosphate separately, or in an integrated manner, said Myong.
"Our work bridges the gap," she said. "We show that it does both in an integrated manner."
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| Contact: Diana Yates diya@illinois.edu 217-333-5802 University of Illinois at Urbana-Champaign Source:Eurekalert |