Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Electrons ’tunnel’ through water molecules between nestled proteins

28.11.2005


Duke University theoretical chemists who spend much of their time calculating how the exotic rules of quantum mechanics govern electrons motion between and through biological molecules have garnered surprising results when they add water to their models.



They have discovered that a scant handful of water molecules positioned in the nearly infinitesimal gap between two "docking" proteins creates unexpectedly favorable conditions for electrons to "tunnel" from one protein to another. The researchers, chemistry professor David Beratan and postdoctoral researchers Jianping Lin and Ilya Balabin, revealed their findings in a paper to be published in the Nov. 25, 2005, issue of the journal Science.

Their work, supported by the National Institutes of Health, delves into puzzling guidelines of physics that Beratan said nature has to follow in order to harness energy and avoid disease.


"Electrons have dual characteristics, sometimes acting like billiard balls and sometimes like waves on a pond," Beratan said in an interview. "As a consequence, electrons do very peculiar things. One thing they can do is tunnel through barriers forbidden to them under the ’classical’ rules of physics.

"Biology has to move electrons through proteins in order to trap energy from the sun, capture energy from our food, and control damage to living systems," he added. "So biology has had to come to terms with this duality. Although electrons have the ability to tunnel, it’s very costly for them. But one thing that proteins seem to do is to guide such electrons from place to place."

Scientists have already deduced that electron movements are enhanced when proteins fold into complex three-dimensional shapes in their active forms. "It is much easier for electrons to tunnel quantum mechanically through a folded protein than it is for them to penetrate empty space," he said.

Beratan said he and other Duke chemists have spent years studying proteins’ roles in electron transport. But only recently has his group addressed how water between protein molecules affects electron movement.

For instance, whenever two proteins that transfer electrons interact strongly -- or "dock" -- they must exchange electrons in a watery medium. What scientists didn’t understand was the role of water at this interface, he said.

According to Beratan, electrons cannot simply hop over the very small half billionths of a meter gaps that separate such docking proteins. Quantum mechanics requires that those electrons instead follow pathways or conduits that are heavily influenced by the positions of nearby atoms and gaps between atoms.

"What our study was about was probing how that tunneling process changes if we begin pulling two proteins apart and the gap between them fills with water," he said.

"What we show is that at the shortest separations electrons take advantage of the proteins in tunneling between those two molecules. But there is an intermediate distance where the proteins are beyond contact and the water molecules start moving into this interface.

"In this intermediate distance before the proteins are too far apart, the water plays a very special role in mediating the electron tunneling more strongly than might have been expected."

An illustration in their Science paper, derived from massive computer studies by the authors, shows how a mere handful of those water molecules can form an organized cluster under the influence of the protein molecules on either side of the gap. This cluster aids the electron transfer process, he said.

Electrons can then tunnel between "donor" atoms at the tip of one protein to "acceptor" atoms on the other protein. Along the way, the electrons follow multiple pathways through these water molecules that facilitate the transport more strongly than expected.

"Before our study, expectations for electron tunneling were that interactions between the electron donor and acceptor through water would drop exponentially as a function of the distance," Beratan said.

"What we found was that water is a better mediator for electron transfer at intermediate distances than anybody had expected. Another finding was that the water-mediated tunneling drops only very slightly as a function of distance within this intermediate length."

The Duke team’s computations show tunneling initially dropping off very rapidly when the proteins first start separating -- just like scientists originally expected. But at intermediate distances of a few tenths of a billionths of a meter "the rates of tunneling don’t change very much," he said. "Then, when the proteins are separated somewhat further, the rates again drop exponentially again as a function of their separation distance," he added.

Experiments in the Netherlands as well as at the University of California, Berkeley also suggest a special role for water in promoting electron transfers between proteins, he said.

"You could think about the structure of the proteins as well as the water as guiding or shepherding the electrons," Beratan said. "So evolution has had to come to terms with physics in the way protein and water direct electrons through complex structures."

The study was the final Ph.D. project for Lin, Beratan’s former graduate student, who is first author of the Science paper. Co-author Balabin helped the group calculate how the naturally occurring motion of atoms in the protein might further influence the electron transfer.

"We see pictures of proteins in fixed positions, but in reality we should think of their atoms as wiggling all over the place," Beratan said.

Monte Basgall | EurekAlert!
Further information:
http://www.duke.edu

More articles from Life Sciences:

nachricht Hunting pathogens at full force
22.03.2017 | Helmholtz-Zentrum für Infektionsforschung

nachricht A 155 carat diamond with 92 mm diameter
22.03.2017 | Universität Augsburg

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Pulverizing electronic waste is green, clean -- and cold

22.03.2017 | Materials Sciences

Astronomers hazard a ride in a 'drifting carousel' to understand pulsating stars

22.03.2017 | Physics and Astronomy

New gel-like coating beefs up the performance of lithium-sulfur batteries

22.03.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>