News Release

Researchers find potential drug screening target for epidemic dengue virus

Peer-Reviewed Publication

Harvard Medical School

BOSTON, MA--Researchers at Children's Hospital Boston and Harvard Medical School have located a vulnerable pocket in the protein that coats the dengue virus, a potentially deadly mosquito-transmitted disease that has been reported in the United States and is commonly found in developing countries. The pocket is located at a pivotal hinge point that could be filled with a small molecule to prevent the protein from folding over into the dangerous shape that allows the virus to infect cells. The discovery, which could speed the search for a drug to treat the disease, is reported in the May 19-23 Proceedings of the National Academy of Sciences Online Early Edition.

Dengue fever and its potentially lethal complication, dengue hemorrhagic fever, have emerged as a major international public health problem found in 100 countries infecting as many 100 million people annually. The U.S. Centers for Disease Control calls dengue the most important mosquito-borne viral disease affecting humans. A tropical disease, dengue outbreaks are possible in Texas and the southeastern United States where dengue cases have been reported and where dengue-transmitting mosquitoes breed in lingering rain water in discarded old tires and crushed beer cans. No vaccine is available.

When a mosquito pokes a hole through the protective layer of the skin for a blood meal, dengue viruses can hitch a ride past the host's first layer of defense. Inside the body, a similar thing happens. A protein – named "E" for the way it envelopes the viral membrane – folds into itself like a fist and somehow punches a hole through the protective membrane of a cell, allowing the virus to enter the cell where it will replicate and spread to other cells.

More specifically, in an infected person's blood stream, the multitasking E-protein shell of a virus latches onto a cell, nuzzles up closer with its viral load, fuses the viral membrane with the cell membrane, and dumps in the viral genes. Dengue E protein achieves all this by performing gymnastic contortions, first stretching then bending. Now, researchers have found a tiny pocket near a likely hinge in the protein that could put a cramp in the protein's calisthenics. If the pocket can be filled with a drug to prop the protein open, the virus may not be able to fuse or infect the cell.

"Inhibiting fusion is a sensible way of inhibiting viral replication," said senior author Stephen Harrison, a Howard Hughes investigator at Children's Hospital Boston, whose group is also working on preventing another sort of viral fusion with HIV, which uses a different mechanism than dengue. The latest HIV drug on the market also targets viral fusion, he said.

"This may turn out to be a false lead, but it suggests an interesting avenue to screen for compounds to inhibit dengue fusion," said Harrison, also a professor of biological chemistry and molecular pharmacology at Harvard Medical School. "In the case of dengue and HIV, we can use structural insights to find small molecule fusion inhibitors."

Harrison is leading a new initiative at Harvard Medical School, the Center for Molecular and Cellular Dynamics (http://focus.hms.harvard.edu/2003/Jan24_2003/structural_biology.html) , which will integrate this kind of information into a coherent picture of how atoms, small molecules, and large protein superstructures move, transfer information, and reconfigure in the crowded, fast-paced life of a cell. The Center reflects a trend in biology to find meaningful ways to integrate the growing "parts list" of genes, proteins, and molecular structures to improve understanding of human health and disease and to display it in useful ways.

This study's findings might apply to the three other types of dengue viruses and to different viruses in the same family with similar envelope proteins, including yellow fever, tick-borne encephalitis, and Japanese encephalitis.

The pocket was discovered in structural biology experiments designed to reveal more details about how the E protein works. Using dengue E protein from Hawaii Biotech, a biopharmaceutical company, Yorgo Modis, a postdoctoral fellow and first author of the paper, and his colleagues found a detergent molecule in a pocket near the hinge in the E protein. A tiny flap in the protein appears to hide the pocket normally. When the pocket is filled, the flap stays open and becomes a piece of scaffolding that keeps the protein propped open at the hinge.

"We didn't know detergents could insert and stabilize the protein assembly," Modis said. "From a practical point of view, detergents don't make good drugs. But knowing the size and shape of the pocket should advance the search for a drug." Modis is now studying the structure of the protein in its shape after the fusion step to learn more details about how the protein's shape change allows the virus to infect cells.

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The research was funded by the Human Frontier Science Program Organization, the National Institutes of Health, and the Howard Hughes Medical Institute.

CHILDREN'S HOSPITAL BOSTON
Children's Hospital Boston is the nation's premier pediatric medical center. Children's has been ranked #1 among the country's pediatric hospitals in U.S. News and World Report for 13 years in a row. Founded in 1869 as a 20-bed hospital for children, today it is a 300-bed comprehensive center for pediatric and adolescent health care grounded in the values of excellence in patient care and sensitivity to the complex needs and diversity of children and families. Children's Hospital Boston is the primary pediatric teaching affiliate of Harvard Medical School, home to the world's leading pediatric research enterprise, and the largest provider of health care to the children of Massachusetts. For more information about the hospital visit: www.childrenshospital.org.

HARVARD MEDICAL SCHOOL
Harvard Medical School has more than 5,000 full-time faculty working in eight academic departments based at the School's Boston quadrangle or in one of 47 academic departments at 17 Harvard teaching hospitals and research institutes. Those Harvard hospitals and research institutions include Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, Cambridge Hospital, Center for Blood Research, Children's Hospital, Dana-Farber Cancer Institute, Harvard Pilgrim Health Care, Joslin Diabetes Center, Judge Baker Children's Center, Massachusetts Eye and Ear Infirmary, Massachusetts General Hospital, Massachusetts Mental Health Center, McLean Hospital, Mount Auburn Hospital, Schepens Eye Research Institute, Spaulding Rehabilitation Hospital, VA Boston Healthcare System.

Contact: John Lacey, 617-432-0442, (public_affairs@hms.harvard.edu), Harvard Medical School
Susan Craig, 617-355-6420, (susan.craig@tch.harvard.edu), Children's Hospital Boston


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