Biology Professor Leads Research to Uncover Mechanisms Viruses Use to Secure and Position Their Genetic Material for Infection

Nature Communications published two papers this month authored by Venigalla Rao, Ph.D., professor of biology; The Catholic University of America’s Bacteriophage Medical Research Center (BMRC), which he directs; and his collaborators. The two papers reveal, in atomic detail, how viruses secure, position, and prepare their genetic material for infection. 

The basic science uncovered in these publications could ultimately help lead to a range of lifesaving biomedical applications for killing antibiotic resistant bacteria, producing anti-viral medications, designing vaccines, and creating gene delivery therapies to treat genetic diseases and cancers.

The researchers studied the bacteriophage T4 to gain this deeper understanding. Rao explained that bacteriophages are used as a model virus, allowing scientists to extrapolate their findings about viral mechanisms across other viruses, many of which cause human disease.

Bacteriophages—literally “bacteria eaters”—are viruses that attach to host bacteria, inject their genome into the host cell and replicate within it, and then kill the bacteria and release newly assembled viruses. Over decades of research, Rao and others had already discovered the basic structure and assembly of the bacteriophage T4. 

The phage’s DNA genetic material is packaged within its shell, or capsid, by a powerful molecular motor. When the packaging is complete, the DNA inside the capsid is under enormous pressure, roughly seven times the pressure in a champagne bottle. The motor is then ejected from the capsid. Neck and tail proteins attach to the capsid to create a fully formed infectious phage virion. 

However, when the packaging motor is ejected, there is a risk that the pressure could release the packaged DNA through the same channel that was used to transport DNA inside. Even a small amount of leakage would render the virus non-infectious. Since  the T4 phage is one of the most infectious viruses known, virologists have been puzzled for decades about how the viral genome is retained without any leakage. 

In the first of their two Nature Communications papers, “Cryo-EM structures of bacteriophage T4 portal-neck assembly intermediates reveal a viral genome retention mechanism,” Rao and his colleagues discovered that the virus assembles two “genome-gates” at the distal (bottom) end of the phage neck. These gates close the channel, prohibiting the DNA from leaking. 

In their second paper, “In situ structures of the portal-neck-tail complex of bacteriophage T4 inform a viral genome positioning mechanism,” the researchers addressed a second question that has perplexed virologists: How is the genome positioned for the next step, the infection of a host cell? 

They discovered that as soon as the neck attaches, a pre-assembled tail docks at the bottom of the neck and expels the lower genome gate while opening the top gate. The channel re-opens, allowing the DNA to descend to the tip of the tail, where it is captured by a “tape measure protein.” 

The genome is then pressure-suspended in the innermost tunnel of the tail tube, spring-loaded and ready for delivery into a new host cell as soon as a signal is received from the fibers at the bottom of the tail that it has the right host to infect, illustrated in this video that accompanied the second article (see supplementary video 7).  

“Our studies revealed unexpected and highly dynamic transitions at atomic precision, captured through a series of remarkably detailed structures,” said Rao. “Understanding these basic mechanisms – how viruses safeguard their genetic material and efficiently deliver it into cells –  is really the key to ultimately engineer future biomedicines.”

Collaborators on the publications with Rao and the BMRC include researchers from Purdue University, Fudan University, and Sun Yat-sen University.