Shape-Shifting Hot Spring Virus Sheds Light on Viral Evolution

Discovery of a viral shape-shifting mechanism could help explain how ancient, rod-shaped viruses evolved into the more complex and formidable spindle-like viruses we see today. The findings have implications for drug and vaccine delivery as well as general understanding how certain viruses evolve.

The study, conducted at University of Virginia, found strange properties exhibited by Sulfolobus monocaudavirus 1 (SMV1), a virus found in harsh environments like volcanic hot springs. Unlike the vast majority of viruses that are either rod-like or spherical, SMV1 is shaped like a spindle. Its protein shell can also grow tails, which the researchers believe is how simpler, rod-like viruses evolved into the spindle-shaped ones seen today.

“We can now understand a new principle in how proteins can form the shell that packages the DNA in a virus,” says lead researcher Edward H. Egelman, PhD, of the University of Virginia (UVA) School of Medicine and UVA’s Department of Biochemistry and Molecular Genetics.

Egelman and his team were able to reveal the strange properties of SMV1 using high-tech cryo-electron microscopy and advanced image processing.  They found that SMV1 contains strands of proteins that slip and slide past each other and were found in both the body and tail of the virus. The strands give the virus a remarkable ability to shapeshift, allowing it to balloon in size to accommodate more genetic material. At the same time, these strands form a barrier to prevent the acid that surrounds them from destroying the DNA inside.

Based on their findings, Egelman and his collaborators conclude that today’s viruses shaped like spindles or lemons likely evolved from ancient rod-shaped ancestors. The rod-shaped viruses could only contain a limited amount of DNA, and the properties that let SMV1 shapeshift would have let ancestral viruses package more genetic material—a useful trait from an evolutionary perspective.

“Viruses can pose great threats to human health, as we see from the COVID-19 pandemic,” says Egelman. “It is thus crucial that we understand more about how viruses have evolved. But we can also learn from viruses, and create new technologies based upon the principles found in these very simple structures.”

The findings were published recently in Cell.