So Srivastava and his UF College of Medicine colleagues decided to test what would happen if they took the phosphate out of the equation.
To do that, the researchers replaced tyrosine with another amino acid, phenylalanine. The two amino acids are identical except for one thing phenylalanine lacks the part that attracts phosphate.
We didnt change anything except the amino acid that does not allow phosphorylation to occur, he said. It was very simple. You can buy a kit from a company and can mutate any amino acid you want.
Tyrosine is found at seven spots on the surface of AAV, Srivastava said. The scientists created seven new vectors, replacing a different tyrosine in each one and inserting in them the gene that triggers production of the blood-clotting protein Factor IX. Patients with hemophilia B, a common form of the disease, do not naturally produce this protein.
In tissue samples and in mice, all the new vectors worked better than a commonly used version of AAV. One of the versions in particular worked 11 times better in tissue samples after 48 hours. In mice, the results were staggering. Two weeks after the mice were injected with the corrective gene, one of the new AAV-gene combos was working 29 times better than the standard vector was at incorporating the new gene into cells, at a 10-fold lower dose.
We were very surprised, Srivastava said. Its amazing to think that changing one amino acid could produce these results.
Now the virus actually completely avoids being phosphorylated, so it doesnt become degraded and it goes into the nucleus, and we get therapeutic levels of proteins. We can generate therapeutic levels of Factor IX.
|Contact: April Frawley Birdwell|
University of Florida