The new research focuses on a protein called banana lectin, or BanLec, that "reads" the sugars on the outside of both viruses and cells.
Five years ago, scientists showed it could keep the virus that causes AIDS from getting into cells - but it also caused side effects that limited its potential use.
Researchers from the University of Michigan in US created a new form of BanLec that fights viruses in mice, but does not have a property that causes irritation and unwanted inflammation.
They succeeded in peeling apart these two functions by carefully studying the molecule in many ways, and pinpointing the tiny part that triggered side effects. Then, they engineered a new version of BanLec, called H84T, by slightly changing the gene that acts as the instruction manual for building it.
The result was a form of BanLec that worked against the viruses that cause AIDS, hepatitis C and influenza in tests in tissue and blood samples - without causing inflammation.
"What we`ve done is exciting because there is potential for BanLec to develop into a broad spectrum antiviral agent, something that is not clinically available to physicians and patients right now," said co-senior author David Markovitz, professor at the University of Michigan Medical School.
"But it`s also exciting to have created it by engineering a lectin molecule for the first time, by understanding and then targeting the structure," said Markovitz.
The researchers used a wide range of tools including X-ray techniques that let them figure out the location of every atom in the original and new forms of BanLec.
Their efforts helped them understand how BanLec connects to both viruses and to sugar molecules on the outside of cells, and how it leads to irritation and other side effects by triggering signals that call in the "first responders" of the body`s immune system.
This understanding is what allowed them to change the gene in a way that fine-tuned the BanLec molecule.
The new one still kept viruses out of cells, but does not have the property that triggers the immune system response. The new version of BanLec has one less tiny spot on its surface for sugars to attach, called a "Greek key" site.
This makes it impossible for sugars on the surface of immune system cells called T cells to attach in multiple spots at once and trigger inflammation.
But it still allows BanLec to grab on to sugars on the surface of viruses and keep them from getting into cells.
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