Virus shells use intentional asymmetry to control RNA release and infection
Viruses are often depicted as tiny, perfectly symmetrical shells that package their genetic material with mathematical precision. Yet new research led by Penn State scientists reveals a deliberate shape imbalance that aids viral infection. This finding not only clarifies a fundamental viral strategy but also opens doors for antiviral drug design and molecular delivery technologies important for vaccines, cancer therapies, drug development, and gene editing.
The team published their results on December 12 in Science Advances and have filed a patent related to the discovery. "A virus lacks sensory organs, so it relies on chemical cues to decide how to replicate its genetic material into new viral packages with precise polarity," explains Ganesh Anand, associate professor of chemistry, biochemistry and molecular biology at Penn State and the study’s lead author. "This polarity governs the RNA—the genetic material that enables infection—and our work shows that asymmetry creates this essential polarity. Viruses embed subtle imperfections in their shells to control how their genetic material is packaged and prepared to exit during infection."
Using state-of-the-art imaging techniques at Penn State’s publicly funded Core Facilities, the researchers examined the architecture of Turnip Crinkle Virus (TCV). TCV is a plant pathogen with an icosahedral—20-sided—shell, a structural motif shared by many human pathogens such as enteroviruses, noroviruses, poliovirus, hepatitis B virus, and the virus that causes chickenpox.
The study found that icosahedral viruses leverage a single chemical bond to bias the internal arrangement of their protein shells, guiding RNA release and host infection. This bond, known as an isopeptide link, ties together two shell-forming proteins and creates a subtle asymmetry that concentrates the RNA on one side of the particle, ensuring the genome exits in a single direction when infecting a host.
Anand likens this to a loaded die in gambling: the virus, like a die weighted on one side, uses this asymmetry to favor a specific outcome. "When the virus disrupts a cell, this prepared design ensures the genetic material bursts out through a defined exit point—rapidly and in the correct direction—so the virus can immediately hijack the host’s machinery to produce more copies," he notes.
A single isopeptide link acts as a molecular hinge, positioning RNA toward one half of the particle and creating a slight imbalance that yields a spring-loaded genome. As the virus enters a cell and begins to disassemble, the RNA is propelled out through the predetermined exit site.
The researchers describe the RNA as not simply floating inside the virus; it is positioned where the plant’s ribosomes—the cell’s protein factories—can grab it, enabling the virus to begin making its own proteins almost immediately, before the plant mounts a defense.
This previously unseen moment—an almost-ready-to-release virus poised for discharge—was captured with two advanced imaging techniques that monitor microscale changes within cells: cryo-electron microscopy and hydrogen-deuterium exchange mass spectrometry.
"We observed the particle’s polarity and found it to be located near where the RNA appears ready to exit," said Varun Venkatakrishnan, a Penn State doctoral student and co-author who led the cryo-EM portion of the work. "This loaded-die mechanism may not be limited to a single plant virus; it could be a universal strategy among similar viruses for packaging themselves."
For human viruses, such as those causing colds or other diseases, RNA release is a critical step. Polio and other enteroviruses rely on precise timing and location to eject RNA inside a host cell. If these viruses could bias that process, as Turnip Crinkle Virus does, they would gain speed and precision to evade immune defenses, Venkatakrishnan explained.
Disrupting RNA release by targeting asymmetrical features like the isopeptide link in Turnip Crinkle Virus could lead to new antiviral therapies or improved RNA-based treatments. This may enable vaccines that release RNA exactly where needed near ribosomes, minimizing degradation and boosting effectiveness, Braet suggested. There’s also potential to enhance RNA expression in plant-virus vectors for therapeutic purposes.
Antiviral drugs could be designed to bind these asymmetrical sites, destabilizing the shell’s shape and preventing the virus from maintaining its spring-loaded state. That would hinder replication and complicate the virus’s ability to evolve resistance within the host, Braet added.
"This is cutting-edge work with promising leads," Anand stated. "We’re excited about where this could lead."
Additional Penn State contributors include undergraduate Molly Clawson, a Schreyer Honors College student majoring in chemistry, and Tatiana Laremore, director of the Proteomics and Mass Spectrometry Core Facility. Contributors from the National University of Singapore include Ranita Ramesh and Sek-Man Wong.
Funding for this research came from the National Institute of General Medical Sciences of the NIH, along with Penn State’s Huck Institutes of the Life Sciences through the Patricia and Stephen Benkovic Research Initiative and the Stephen and Patricia Benkovic Summer Research Award in Chemistry.
