"We had the structures and sequences of both BK and SV40, and they are relatively similar in their amino acid identity," Allen said. "So when you see minute differences between them, you can target these differences to ask whether this difference allows for different infection in different hosts."
Sure enough, when Allen made the change at amino acid site 68 in the BK polyomavirus, it switched from binding the "ganglioside" sugar GD3 to binding with GM1.
Allen and colleagues tested this not only in cells in the lab, but also by dropping the viruses onto microarrays of binding target sugars.
And for even more confirmation, the Brown scientists sent the mutated BK viruses back to Germany for more NMR resolution.
"The NMR spectrum of the BK and the SV40 were identical," Atwood said, "They thought they had mixed up the samples. They were identical in terms of their ability to bind to GM1, the monkey receptor."
It may take several steps beyond a switch of receptor preference for a virus to infect new cells in the body or entirely new species, but such a switch could be a key step in more viruses than just the polyomavirus family, the scientists said. Others seem to switch preferences fairly quickly.
"Prominent examples include different serotypes of adenoviruses, the canine and feline paroviruses, as well as avian, swine, and human influenza viruses," they wrote in PLOS Pathogens.
|Contact: David Orenstein|