Natural GMOs Part 272. Cells Talk in a Language That Looks Like Viruses | Quanta Magazine

Raw Materials for Evolution

When the neuroscientist Jason Shepherd and his postdoc Elissa Pastuzyn at the University of Utah began trying to decode the detailed structure of the Arc protein, they knew nothing about extracellular vesicles. What they did know was that mice lacking the Arc gene were unable to learn from scary situations—a deadly defect for an animal that’s a snack-size morsel for many predators. What’s more, another lab had already forged ahead with a less-detailed structure of the protein, and they were strongly motivated to publish a more detailed paper on Arc.

As Pastuzyn repeatedly tried to purify Arc, however, the single protein kept self-assembling into a more complex structure. At first, everyone thought it was a mistake. But when it kept happening, Shepherd and Pastuzyn took a peek under the electron microscope. The protein structure looked familiar.

“It looked like a virus,” she said. “It was a double-ringed structure, and the resemblance was uncanny. I had no idea that’s what it was.”

When Pastuzyn looked up the DNA sequence of Arc in GenBank (the NIH’s depository for all gene sequences), she discovered that the predicted structure of Arc most closely resembled that of Gag, a protein that forms a retrovirus’s capsid shell, which is subsequently encased in a host-derived lipid membrane.

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