Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

For unzipping DNA mysteries -- literally -- Cornell physicists discover how a vital enzyme works

19.09.2011
With an eye toward understanding DNA replication, Cornell researchers have learned how a helicase enzyme works to actually unzip the two strands of DNA. (Nature, online Sept. 18, 2011.)

At the heart of many metabolic processes, including DNA replication, are enzymes called helicases. Acting like motors, these proteins travel along one side of double-stranded DNA, prompting the strands to "zip" apart.

What had been a mystery was the exact mechanics of this vital biological process – how individual helicase subunits coordinate and physically cause the unzipping mechanism.

Cornell researchers led by Michelle Wang, professor of physics and an investigator of the Howard Hughes Medical Institute (HHMI), have observed these processes by manipulating single DNA molecules to watch what happens when helicases encounter them, and how different nucleotides that fuel the reactions affect the process. For their experiments they used an E. coli T7 phage helicase, a type with six distinct subunits, which is a good representation of how many helicases work.

"This is a great demonstration of the power of single-molecule studies," said Wang, whose lab specializes in a technique called optical trapping. To record data from single molecules, the scientists use a focused beam of light to "trap" microspheres attached to the molecules.

Prior to this work, researchers from other labs had found that the nucleotide dTTP (deoxythymidine triphosphate) was a "preferred" fuel for the helicase, and that the helicase apparently wouldn't unzip DNA if ATP (adenosine triphosphate) was provided as fuel. Wang and her colleagues found this puzzling, because ATP is known to be the primary fuel molecule in living organisms.

In their latest work, they discovered that, in fact, ATP does cause unwinding, but only in the single-molecule study could they confirm this. In normal biochemical studies, ATP doesn't seem to work, because it causes helicase to "slip" backward on the DNA, then move forward, then slip again.

In bulk studies, rather than single-molecule kinetic observations, the ATP doesn't produce a signal from unwound DNA because the slippage masks the signal.

They then surmised that different mixtures of nucleotides might allow them to investigate helicase subunit coordination. They found that very small amounts of dTTP mixed with large amounts of ATP were enough to decrease the "slippage" events they saw with the ATP alone.

Further inspection revealed that while two subunits of the T7 helicase are binding and releasing nucleotides, the other four can remain bound to nucleotides to anchor the DNA and prevent it from slipping. It only takes one subunit bound to dTTP to decrease slippage almost entirely – a little goes a long way.

Such studies can help scientists gain a deeper understanding of helicase mechanics and, in the case of medicine, what happens when helicases go awry or don't bind correctly.

Smita Patel, Rutgers University biochemistry professor and paper co-author, says helicase defects are associated with cancer predisposition, premature aging and many other genetics-related conditions.

"This study provides fundamental new knowledge about a cellular process that is essential to all forms of life," said Catherine Lewis, who oversees single-molecule biophysics grants at the National Institute of General Medical Sciences of the National Institutes of Health. "By using single-molecule methods to study how helicases work, Dr. Wang has resolved several longstanding questions about how the enzyme is coordinated, and possibly regulated, during replication."

Along with contributions from researchers at other institutions, the paper's two lead authors are Bo Sun, an HHMI and Cornell postdoctoral associate in physics, and Daniel S. Johnson, a former graduate student.

The Nature paper, "ATP-induced helicase slippage reveals highly coordinated subunits," was funded by the National Institutes of Health, the National Science Foundation and the Cornell Molecular Biophysics Training Grant.

Blaine Friedlander | EurekAlert!
Further information:
http://www.cornell.edu

More articles from Life Sciences:

nachricht One step closer to reality
20.04.2018 | Max-Planck-Institut für Entwicklungsbiologie

nachricht The dark side of cichlid fish: from cannibal to caregiver
20.04.2018 | Veterinärmedizinische Universität Wien

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Magnetic nano-imaging on a table top

20.04.2018 | Physics and Astronomy

Start of work for the world's largest electric truck

20.04.2018 | Interdisciplinary Research

Atoms may hum a tune from grand cosmic symphony

20.04.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>