Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study suggests enzyme crucial to DNA replication may provide potent anti-cancer drug target

15.04.2011
Elegant crystal structures depict sophisticated machine for cutting DNA

An enzyme essential for DNA replication and repair in humans works in a way that might be exploited as anti-cancer therapy, say researchers at The Scripps Research Institute and Lawrence Berkeley National Laboratory.

The research, published in the April 15, 2011 issue of the journal Cell, focused on a member of a group of enzymes called flap endonucleases, which are essential to the life of a cell. The findings show new, clearly defined crystal structures of the enzyme FEN1 in action—demonstrating it functions in a way opposite to accepted dogma.

"This work represents a seminal advance in the understanding of FEN1," said team leader John Tainer, professor and member of the Skaggs Institute for Chemical Biology at Scripps Research and senior scientist at Lawrence Berkeley National Lab. "The research produced very accurate structures showing DNA before and after being cut by FEN1 activity, providing a basis for understanding a whole superfamily of enzymes that must cut specific DNA structures in order for DNA to be replicated and repaired."

This superfamily includes important targets for the development of new cancer interventions, Tainer added. Many cancers show high levels of FEN1 expression, which in some cases is correlated to tumor aggression. For these cases, FEN1-specific inhibitors may have chemotherapeutic potential.

"A better understanding of FEN1 structure and function may have long-term positive benefits to human health," noted co-author Andy Arvai, a scientific associate at Scripps Research.

Working rapidly with exquisite precision

In order for DNA to replicate, it has to unwind its double helix, which is formed out of two strands of amino acids coiled together. This unwinding is done by a replication fork whereby the two strands are separated. These strands, which form two branching prongs of the replication fork, serves as a template for production of a new complementary strand.

That task is fairly straightforward on what is known as the "leading" of the two strands. The replication fork moves along from the so-called 3' (three prime) end to the 5' (five prime) end, and DNA polymerase synthesizes a 5' to 3' complementary strand.

But because the two strands are anti-parallel, meaning they are oriented in opposite directions, the work of DNA polymerase, which can only work in the 5' to 3' direction, is more difficult on the so-called lagging strand. This strand needs to be replicated in pieces, which are known as Okazaki fragments, located near the replication fork. These fragments include a "primer," a strand of RNA that serves as a starting point for DNA synthesis.

This is where FEN1 comes in—it removes that RNA primer on the 5' flap, which occurs every 100 base pairs or so on the lagging strand, said Tainer. It's an enormous job that has to be done rapidly and accurately in order to glue the ends of replicated DNA on the lagging strand together to eventually provide an intact chromosome. "To replicate one DNA double helix in one cell you have to cut off a 5' flap so that you don't have one base pair too many or one base pair too few, and you have to do this accurately with 50 million Okazaki primers in each cell cycle," Tainer said. "It has always been a mystery as to how FEN1 can precisely cut this flap so efficiently and so rapidly. It's an amazing, efficient molecular machine for precisely cutting DNA."

To determine what FEN1 looked like in action, Arvai led the difficult but ultimately successful effort to grow crystals of the human FEN1 protein bound to DNA. The team then used X-ray crystallography to determine the atomic structure of the complex. Using Lawrence Berkeley National Laboratory's Advanced Light Source beamline, called SIBYLS, the scientists solved three different crystal structures.

The end result was a highly detailed and accurate model showing the structures of DNA before and after being cut by FEN1.

Earlier crystal structures suggested that FEN1 first grabs onto the flap of the 5' single stranded DNA, slides down to the joint where DNA is duplicated, and cuts and patches the primer there. But the new study found that, in fact, FEN1 binds, bends, frays, and then cuts the DNA.

"It binds duplex DNA, bends it into a single-stranded DNA right at the flap, flips out two base pairs, and cuts between them," said Tainer. "This gives FEN1 very precise control—a sophistication we had not expected."

Clues to cancer control

Researchers know that mutations in FEN1 can predispose humans to cancer growth because errors in flap removal can create unstable DNA that promotes cell growth and division. And studies in mice have shown that when one of two inherited FEN1 genes are knocked out, the mice are predisposed to cancer development if their DNA is damaged.

While other DNA repair systems can help compensate for FEN1 mistakes, or for missing FEN1 activity, "you need a lot of FEN1 for DNA repair and replication to work properly," Tainer said.

This suggests that, in tumors already missing one set of repair proteins, selectively inhibiting the function of FEN1 in rapidly replicating cells may prove to be an effective anti-cancer therapy. "The Achilles heel of cancer cells is defective DNA repair pathways," said Tainer, "because that makes them more sensitive to traditional therapies, such as chemotherapy and radiation. If cancer can't repair the damage these therapies do to tumors, they will die."

This is the paradox of DNA repair: while a defect in DNA repair can cause cancer, knocking out a number of backup repair systems may make tumors vulnerable to anti-cancer therapies.

"My hope is that our finding of how FEN1 works mechanistically might provide a foundation for a next-generation cancer drug," said Tainer. "We need to cut as many lifelines as possible in cancer cells in order to provide an effective treatment."

The study was supported by grants from the National Institutes of Health and the Biotechnology and Biological Sciences Research Council (BBSRC) in the United Kingdom.

First authors of the paper, "Human Flap Endonuclease Structures, DNA Double-Base Flipping, and a Unified Understanding of the FEN1 Superfamily," are Susan E. Tsutakawa and Scott Classen of Lawrence Berkeley National Laboratory and Brian R. Chapados and Arvai of Scripps Research. In addition to Tainer, Tsutakawa, Classen, Chapados, and Arvai, authors are: L. David Finger currently at the University of Sheffield; Grant Guenther of Scripps Research; Christopher G Tomlinson, Peter Thompson, and Jane A. Grasby of the University of Sheffield; Altaf H. Sarker and Priscilla K. Cooper of Lawrence Berkeley National Laboratory; Binghui Shen of City of Hope National Medical Center and Beckman Research Institute and Zhejiang University (China).

About The Scripps Research Institute

The Scripps Research Institute is one of the world's largest independent, non-profit biomedical research organizations. Scripps Research is internationally recognized for its discoveries in immunology, molecular and cellular biology, chemistry, neuroscience, and vaccine development, as well as for its insights into autoimmune, cardiovascular, and infectious disease. Headquartered in La Jolla, California, the institute also includes a campus in Jupiter, Florida, where scientists focus on drug discovery and technology development in addition to basic biomedical science. Scripps Research currently employs about 3,000 scientists, staff, postdoctoral fellows, and graduate students on its two campuses. The institute's graduate program, which awards Ph.D. degrees in biology and chemistry, is ranked among the top ten such programs in the nation. For more information, see www.scripps.edu .

Mika Ono | EurekAlert!
Further information:
http://www.scripps.edu

More articles from Life Sciences:

nachricht New catalyst controls activation of a carbon-hydrogen bond
21.11.2017 | Emory Health Sciences

nachricht The main switch
21.11.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>