Researchers at the University of Pennsylvania School of Medicine have determined the structure of an important smallpox virus enzyme and how it binds to DNA. The enzyme, called a topoisomerase, is an important drug target for coming up with new ways to fight smallpox. The researchers present their findings in the August 4 issue of Molecular Cell.
"This enzyme is one of the most closely studied DNA-modifying enzymes in biology," says Frederic D. Bushman, PhD, Professor of Microbiology, one of the senior authors. "The structure of the DNA complex has been long-awaited." DNA-modifying enzymes bind to specific sequences in the genetic code to aid in the many steps of DNA replication.
The smallpox virus is one of the most easily transmissible infectious diseases known to humans, resulting in up to 30 percent mortality. The efficiency with which it spreads, combined with the deadly nature of the disease, has raised fears that smallpox could be revived for use in bioterrorism. Knowing the exact three-dimensional structure of smallpox virus proteins could help researchers design antiviral agents, but few structures of whole viral proteins exist.
Poxviruses are large viruses that contain two strands of DNA and replicate themselves entirely in the cytoplasm of infected cells. Poxviruses do not take over the genetic machinery inside the nucleus of the host cell, as many viruses do. Because of this strategy, poxviruses encode many of the enzymes they need to replicate their own genes, and hence reproduce. One of these enzymes is a topoisomerase, which is used by the virus to relieve the excessive twisting of DNA strands that normally occurs during DNA replication and transcription of the viral genes. Upon initial infection, the poxviruses come already equipped with some proteins, including topoisomerases, to kick-start replication.
The structure was determined in a collaborative effort between the Bushman lab and the lab of the other senior author Gregory D. Van Duyne, 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.
Karen Kreeger | EurekAlert!
Molecular libraries for organic light-emitting diodes
24.04.2017 | Goethe-Universität Frankfurt am Main
Fine organic particles in the atmosphere are more often solid glass beads than liquid oil droplets
21.04.2017 | Max-Planck-Institut für Chemie
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
24.04.2017 | Trade Fair News
21.04.2017 | Physics and Astronomy
21.04.2017 | Health and Medicine