Human DNA is not always making us function in ways we understand. Some of our genome is just there, and we’re not sure what it does. In fact, 8% of our DNA are viruses our ancestors caught one day and passed down to us.
These retroviruses have been called ghost viruses, or viral detritus.
“Dark matter in our genomes. Remnants of our evolution,” said Erica Ollmann Saphire, professor and CEO of the La Jolla Institute for Immunology. “These things were integrated hundreds of thousands of years ago and they’re still present.”
The viruses that become part of our genome have a clever trick they can play.
“Retroviruses are also viruses but they have this little ability to copy themselves into our DNA. So instead of disappearing they’re actually with us forever,” said Jeremy Shek, a biology post doctoral fellow at the La Jolla Institute for Immunology who’s been studying retroviruses.
Typically, we carry the viruses in our genomes and somehow we manage to silence them. But it turns out those ghosts can be reawakened when we get sick.
“In a lot of diseases, such as cancers, autoimmune diseases, and neurodegenerative disorders, for example, we actually see that these ancient, fossil retroviruses, these ghosts, some pieces of them still show up,” Shek said.
Shek devoted his Ph.D. to the subject of these retroviruses and their proteins. He also led the study that was published in Science Advances. The viruses are called HERV’s, which stands for Human Endogenous Retrovirus.
The involvement of HERV proteins with disease is well known. The proteins, which do the work of a virus, have been seen parked on the surface of cancerous tumor cells.
Researchers at La Jolla Institute have created a precise picture of what they call the HERV-K envelope protein, using a powerful electron microscope, revealing its appearance and structure. This was a challenge since these proteins change shape, or fold, very quickly.
“You can look at them funny, and they’ll unfold,” Shek said.
But they found a way to freeze them in time in order to see them through the microscope.
“Which then takes images of these proteins. Thousands of images. And we look at thousands of individual copies of these proteins, from all different angles. And from there we can reconstruct a 3D view of what these proteins might look like,” he said.
The proteins allow the virus to enter a cell and make us sick. And knowing what it looks like reveals its functions and can tell you how an antibody can bind to it and disable it. We don’t yet know the exact role of these inherited viruses in diseases.
HIV, which causes AIDS, is another retrovirus. That one also becomes part of our DNA but, thankfully, is not passed on to our descendants.
