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Temperature, mobility may be clues to taming some viruses

November 24, 2014


PITTSBURGH ó Studies by a Carnegie Mellon University lab have shown that some viruses violently expel their DNA inside human cells when the virus reaches body temperature, and that it might be possible to stop the spread of infection by interrupting that process.

Research by CMU biophysicist Alex Evilevitch and his team demonstrated for the first time how the DNA packaged inside viruses shifts from being stiffly inflexible to becoming loose and active when the virus approaches 98.6 degrees.

In one study involving the herpes simplex virus, which affects hundreds of millions of people worldwide, the researchers also found that negative electrical charges in the viral DNA accelerated its explosion into human cells.

The studies raise the possibility that it might be possible to treat viral infections by controlling this transition in the mobility of viral DNA.

Akiko Iwasaki, an immunobiology researcher at the Yale School of Medicine, who was not involved in the studies, said the results suggest that "locking the viral DNA in the solid state would be beneficial in the prevention of infection. If we can find a virological agent that does that, it might be a prevention treatment."

Evilevitch said his labís fundamental discoveries about viral replication were made possible by sophisticated equipment, including an atomic force microscope that uses a minuscule needle to measure the surface features of viral DNA. Those measurements allowed the lab to discover that before the virus reaches body temperature, its DNA is still and inflexible.

When first designing the research, about five years ago, Evilevitch said his lab was hoping to discover something about temperatureís role in the DNA transfer.

"Temperature is rarely varied ... in most biophysical measurements in viruses. Itís a new and rapidly developing field in virology." New instruments are available and, he said, "a lot of times studies were done on the virus, not the single cell. We realized there were no studies on the structure of DNA in viruses, very few, and those that are done are done with cryo-electron microscopy and freezing the viruses."

Evilevitch said a better understanding of viruses was needed. "Before we have a medical application in mind, first we have to know how viruses work."

The team recently published two studies on their findings.

In the Proceedings of the National Academy of Sciences, the team reported on their work with a virus that infects E. coli, a bacteria that can cause severe diarrhea in people. This was the one that found body temperature influenced the activity of the DNA strands.

In Nature Chemical Biology, the teamís study of herpes simplex virus type 1 found that the similar solid-to-fluid DNA transition also occurred at body temperature, and also was linked to the ionic conditions (affecting electrical charges and the mobility of DNA strands) in epithelial and neuronal cells that are attacked by the herpes virus.

Epithelial cells cover the inner and outer surfaces of the body and its organs; neuronal cells are in the brain, spinal cord and nerves.

Herpes simplex virus is a challenge particularly for immune-compromised patients, such as newborn babies and cancer and HIV patients. Longtime use of antiviral medications can lead to resistance. "Mutations develop faster in immune-suppressed people," Evilevitch said.

The virus lies latent in neuronal cells. "The neuronal cells undergo wide variations of activity controlled by ion concentration," he said. "We found that this affects the state of the DNA in herpes capsid, affecting the ability of the virus to release its DNA into the cell and its ability to multiply." Virologist Fred Homa at the University of Pittsburgh School of Medicine also participated in the study.

Evilevitch said although the antiviral drug Acyclovir is very effective in treating herpes, "eventually the patient will develop resistance to the drug."

The herpes virus is challenging to get under control, agreed Yale researcher Iwasaki. "Acyclovir doesnít cure the disease. It just prevents the replication of the virus at the time of the drug treatment. It needs to be continuously treated."

She added that, "Chipping away at any of these aspects of the viral life cycle is important." Further research, she said, might shed more light on how the virus expels the DNA strands with an intense, rapid force into the host cell nucleus.

"It might help us understand how the host might recognize, or avoid the recognition, of the virus," she said. "Perhaps this sort of ejection of the viral DNA might be rejected by the host, somehow this might be recognized by the innate immune system."

 

 


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