Protein receptor substitution enables bat coronaviras to grow well in monkey cells, says PNAS study.
The severe acute respiratory syndrome coronavirus (SARS-CoV) outbreak five years ago sickened more than 8,000 people and killed nearly 800. Investigators now believe the virus may have been transferred to humans via bats, though the actual animal source is not definitive and bat coronaviruses had never been successfully grown in culture or animals.
Researchers used published SARS-like bat coronavirus sequences to establish a genome sequence that became the best bet for a virus genome that would be viable. They then used commercial DNA synthesis and reverse genetics to build the consensus viral genome and several variations.
The consensus synthetic SARS-like bat CoV did not initially grow in culture. But substitution of a single small region from human SARS-CoV, the Spike protein receptor binding domain that is critical for viral entry into human cells, allowed the new chimeric SARS-like bat CoV to grow well in monkey cells.
The chimeric virus also grew well in mouse cells modified to express the receptor for SARS-CoV and in primary human airway epithelial cells. It grew poorly in mice, but a single additional change in the Spike region allowed efficient growth in mice, without causing a SARS-like disease.
The findings identify pathways by which a bat coronavirus may have adapted to infect humans, and suggest that a very simple recombination event may have been enough to allow a coronavirus to move from one species to another because after a virus gains the capacity to jump species, additional simple adaptations may be adequate to increase its ability to grow in the new animal host.
Research with all bat viruses, even weakened mutants, was performed under the same stringent biosafety conditions used to study virulent SARS-CoV. The investigators found that human antibodies known to render SARS-CoV noninfectious also neutralized the bat SARS-like coronavirus, providing an additional safety measure. The studies also provide a model approach for rapid identification, analysis, and public health responses to future natural or intentional virus epidemics.
Scientists from Vanderbilt University Medical Center and the University of North Carolina at Chapel Hill collaborated on the effort, which was published online in Proceedings of the National Academy of Sciences on November 24.