Viruses, often described as perfectly geometric shells that encapsulate genetic material, may in fact rely on subtle asymmetry to enhance their ability to infect hosts, according to new research from Penn State scientists. The study, published December 12 in Science Advances, details how this imbalance aids viruses in releasing RNA and controlling infection.
"A virus lacks sensory organs, so it uses chemical cues to determine how it replicates its genetic material into new viral packages or assemblies with precise polarity," said Ganesh Anand, associate professor of chemistry, biochemistry and molecular biology at Penn State and lead author on the study. "This polarity guides the RNA, its genetic material that allows the virus infection to spread, and our research shows that asymmetry is what gives the virus this essential polarity. Viruses build these subtle imperfections into their shells to control how and where their genetic material is packaged and poised to exit during an infection."
The researchers focused on the Turnip Crinkle Virus (TCV), a plant pathogen with a shell structure similar to many human viruses such as enteroviruses and noroviruses. Using advanced imaging techniques at Penn State's Core Facilities, they discovered that a single chemical bond—an isopeptide link—creates a slight asymmetry in the viral shell. This bond connects two structural proteins, clustering the virus’s RNA on one side of the particle so it exits through a specific point when infecting a host.
Anand likened this mechanism to a "loaded die," explaining: "When the virus enters a cell and begins to break apart, this 'loaded die' design ensures the genetic material bursts out through a specific exit point - fast and in the right direction - so it can immediately hijack the host's machinery to make more virus."
He added that just one isopeptide link produces this effect by acting as a molecular hinge or strap: "The RNA doesn't just float around," Anand said. "It's positioned right where the plant's ribosomes, its protein-makers, can grab it. This lets the virus start making its own proteins immediately, before the plant can mount a defense."
The team visualized this process using cryo-electron microscopy and hydrogen-deuterium exchange mass spectrometry. Varun Venkatakrishnan, Penn State doctoral student and co-author who led cryo-electron microscopy work for this study, said: "We were able see the polarity of the particle and it appeared to be positioned somewhere very close to where the RNA looked like it was wanting to get out. This 'loaded die' mechanism that we discovered isn't just a plant virus trick. It could be a universal strategy for how these types of viruses package themselves."
Sean Braet, postdoctoral researcher at Penn State and co-author on the paper, explained potential applications: "This could mean designing vaccines that release RNA exactly where it's needed, near protein-making machinery, to reduce degradation and boost effectiveness of the vaccine. There is a specific feature on the RNA that can help to direct this process, and now, we're in the process of figuring out if we can use this naturally occurring phenomena to the advantage of cost-efficiently amplifying expression of therapeutic RNAs in plant virus vectors."
Braet also noted implications for antiviral drug development: antivirals could target these asymmetric sites within viral shells—such as oseltamivir does for influenza—to destabilize them and hinder replication.
"All of this research is very cutting edge and is going on right now," Anand said. "We have some promising leads."
Other contributors from Penn State include Molly Clawson; Tatiana Laremore; Ranita Ramesh; Sek-Man Wong from National University of Singapore; with funding provided by U.S. National Institutes of Health’s National Institute of General Medical Sciences as well as support from Penn State’s Huck Institutes of Life Sciences.
