( PhD Professor of Biochemistry and Bio...)Penn Researchers Throw Light on the Structure Of Smallpox Virus Protein,Health

PhD, Professor of Biochemistry and Biophysics and an Investigator with the Howard Hughes Medical Institute (HHMI). Using purified topoisomerase enzyme that had been expressed in bacterial cells, they bound the enzyme to short segments of DNA that contained the viral topoisomerase's specific recognition sequence. They then determined the three-dimensional structure of the topoisomerase-DNA complex using X-ray crystallography.

One of the primary differences between the viral topoisomerase enzyme and the closely related human enzyme that functions in the nucleus of all human cells is that the viral enzyme only relaxes supercoiled DNA when it binds to specific DNA sequences. The structure of the poxvirus topoisomerase-DNA complex provides some important clues about how this recognition and activation mechanism works.

"The more the viral enzyme differs from the human nuclear enzyme, the more likely it is that inhibitors could be developed that are specific to the viral enzymes," says Bushman.

Knowing the three-dimensional structure of the smallpox virus topoisomerase-DNA complex will also facilitate the design of agents to combat poxvirus infections. Topoisomerases are some of the most widely targeted proteins by drugs that are intended to inhibit growth of the cell. Drugs that target topoisomerases generally stabilize an intermediate of the enzyme's reaction in which one of the DNA strands is broken. If these breaks are not repaired, the DNA cannot be replicated and the cell dies.

In the case of smallpox virus, the hope is that drugs targeted to the viral topoisomerase enzyme will prevent viral replication through a similar mechanism. The X-ray structure provides a template for designing small molecules that could stabilize the broken DNA in the intermediate form, thereby killing smallpox virus particles.

(Source: EurekaAlert)
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