By designing a small piece of protein, or peptide, that can prevent human parainfluenza viruses from attaching to cells, researchers have improved a method in rodent models to help children stay healthy.
Human parainfluenza viruses, or HPIV, are the leading cause of childhood respiratory infections, responsible for 30% to 40% of illnesses like croup and pneumonia. Viruses also affect the elderly and people with weakened immune systems.
To make people sick, HPIVs have to attach themselves to cells and inject their genetic material to start making new viruses. HPIV3 is the most common among these viruses. There are currently no approved vaccines or antivirals for HPIV3 infection in humans.
In a study conducted by the Sam Gellman lab of the University of Wisconsin-Madison’s Department of Chemistry and the lab of Anne Moscona and Matteo Porotto at Columbia University, researchers drew on years of work on the treatments. peptides to generate one capable of blocking the HPIV3 Attachment Process.
The researchers published their results on April 7 in the Journal of the American Chemical Society.
To enter host cells, HPIVs use specialized fusion proteins that look like three corkscrews placed side by side. Previous work from the Moscona-Porotto lab has shown that scientists can part part of this corkscrew protein from HPIV3, introduce this peptide into the virus, and prevent the corkscrew from driving the infection process. The peptide, itself a corkscrew, essentially closes with the virus’s corkscrews, creating a tight bundle of six corkscrew shapes.
The new peptide persists in the body longer, making it about three times more effective at blocking infection in rodent models of the disease than the original form.
The research team began by trying to design the original peptide to be more resistant to protein digesting enzymes in the body, which can easily shred proteins and render them useless. So the Gellman lab turned to unusual building blocks to create a stronger peptide.
Cells build proteins from alpha amino acids. But chemists can create beta amino acids, which are similar but have an extra carbon atom. When peptides use these building blocks of beta amino acids, they often take on a different shape due to the extra atom. This can help a peptide hide from protein digesting enzymes and survive longer.
However, the researchers also knew that if the shape of the peptide changed too much due to these unusual building blocks, they might not lock in with the HPIV corkscrew fusion protein.
This is where Gellman’s decades of experience in testing and modifying peptides containing beta-amino acids became essential.
“We know which side of the peptide binds to its target protein. So we (knew we) can only modify the residues that are not directly involved in the binding of the viral protein, ”explains Victor Outlaw, postdoctoral researcher in the lab and one of the co-first authors of the report. In lab tests, they found that the carefully modified peptide still binds strongly to the virus protein.
In another improvement launched by the Moscona-Porotto laboratory, scientists hooked the peptide to a cholesterol molecule. This fatty addition helps the peptide slide into the fatty cell membrane, where it can best block the virus.
“Our hypothesis was that the combination of beta-amino acids and cholesterol would increase antiviral effectiveness,” explains Outlaw, who explained that cholesterol helps get the peptide where it needed to go, while the shape change by compared to beta-amino acids allowed the peptide to persist longer in the body.
As the research team hoped, when they gave the new peptide to cotton rats, it lasted much longer in the lungs than the previous version, thanks to its resistance to digestion by enzymes. The peptide was administered into the noses of rats.
To test the effectiveness of the peptide in preventing infection, cotton rats were given the new peptide before being exposed to HPIV3. Compared to animals that received no antiviral peptide, those that received the improved peptide had 10 times less virus in their lungs.
And compared to the peptide which was more sensitive to enzymes, the more resistant peptide reduced viral load by about three times, suggesting that the new peptide’s ability to bypass digestion in the body helps it block it better. infection.
While the approach has yet to be tested in humans and researchers need to refine and test the system further, it provides a new strategy to potentially prevent or treat these common infections.
The research collaboration is now looking to make second-generation peptides that last even longer in the body. They also want to test the ability of the modified peptide to block infection with related viruses. This additional research could bring peptide therapy closer to clinical trials.
“It was a very lucky gathering of groups who had complementary needs and abilities,” Gellman says. “It was truly a great joint effort.”
This work was supported by the National Institutes of Health (grants R01AI114736, R01 GM056414, F32 GM122263, and T32 GM008349.)