Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

For Unzipping DNA Mysteries – Literally – Physicists Discover How a Vital Enzyme Works

20.09.2011
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, a biochemistry professor at the Robert Wood Johnson Medical School, at the University of Medicine and Dentistry of New Jersey, and paper collaborator, 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 | Newswise Science News
Further information:
http://www.cornell.edu

More articles from Physics and Astronomy:

nachricht Nanostructures taste the rainbow
29.06.2017 | California Institute of Technology

nachricht X-ray photoelectron spectroscopy under real ambient pressure conditions
28.06.2017 | National Institutes of Natural Sciences

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Making Waves

Computer scientists use wave packet theory to develop realistic, detailed water wave simulations in real time. Their results will be presented at this year’s SIGGRAPH conference.

Think about the last time you were at a lake, river, or the ocean. Remember the ripples of the water, the waves crashing against the rocks, the wake following...

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Nanostructures taste the rainbow

29.06.2017 | Physics and Astronomy

New technique unveils 'matrix' inside tissues and tumors

29.06.2017 | Life Sciences

Cystic fibrosis alters the structure of mucus in airways

29.06.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>