RNA Polymerase Mutation Stabilizes Live Virus Vaccines

By LabMedica International staff writers
Posted on 28 Jul 2016

A team of molecular virologists has developed a more effective method for attenuating the replicative capabilities of the coxsackievirus and is using this platform to develop a vaccine for it and other positive-sense single-stranded RNA viruses, a group that includes poliovirus, dengue, and Zika.

During a previous study on coxsackievirus replication, investigators at Colorado State University (Fort Collins, USA) found that when the coxsakievirus RNA-dependent RNA polymerase copied the viral genome, it made three or four random mistakes that allowed the virus to continually evolve and survive.

Image: An atomic-level structural model of coxsackievirus B3 polymerase, which is responsible for making copies of the virus genome. The researchers replaced the orange phenylalanine 364 that is found in two different positions, with the turquoise tryptophan that is larger and covers both positions without needing to move. This causes fewer mutations to be made and reduces the ability of the virus to replicate and cause disease (Photo courtesy of Dr. Olve Peersen, Colorado State University).

To establish stable, attenuated mutant strains that could be used for vaccination without danger of back mutation reestablishing full viral pathogenicity, the investigators introduced mutations into the RNA-dependent RNA polymerase.

They reported in the July 1, 2016, issue of The Journal of Biological Chemistry that they had exchanged a phenylalanine molecule in the RNA polymerase with tryptophan. The tryptophan residue caused the polymerase to make fewer mutations, and this reduced the ability of the virus to replicate and cause disease. Back mutations prevented the virus from replicating at all, resulting in its elimination from the host organism.

"We think it is going to work, but we have to show that it will," said senior author Dr. Olve Peersen, professor of biochemistry and molecular biology at Colorado State University. "Trying to outsmart Mother Nature is pretty daunting, especially in these viruses. There are ways that things happen you never anticipate, and the virus finds a way to survive."

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Colorado State University