Proteins keep cells humming. Some are enzymes that taxi electrons to chemicals outside the cell, to discharge excess energy generated during metabolism. This maintains energy flow in the cell and, in turn, keeps the cell alive.
Artist's depiction of purified, electrified bacterial cell outer membrane protein binding with and passing electrons to the iron-rich mineral hematite. In this purified-protein fuel cell, the seal made by the protein coating on the electrode effectively acts in place of a membrane necessary in whole-organism biofuel cells. Eliminating the membrane could aid the design of bioreactors to power small electronic devices. Credit: Pacific Northwest National Laboratory
The process has worked a little like that slogan for a hyper-electrified desert gambling town: What happens in the cellular environs stays there.
Now, scientists for the first time have observed this electricity-shuttling process taking place sans cells, in purified proteins removed from the outer membrane of the versatile, metal-altering soil bacterium Shewanella oneidensis. Reporting in the current advance online edition of the Journal of the American Chemical Society, they suggest that proteins rendered portable from the organisms that spawned them could make miniature bioreactor cells feasible.
"We show that you can directly transfer electrons to a mineral using a purified protein, and I don't think anyone had shown that before," said Thomas Squier, senior author and lab fellow at the Department of Energy's Pacific Northwest National Laboratory.
The feat is the bacterial equivalent of removing lungs and coaxing the disembodied tissue to breathe.
Squier and principal authors Yijia Xiong and Liang Shi, PNNL staff scientists, discovered that the proteins, outer membrane c-type cytochrome A, or OmcA, formed a dense coating on the iron-rich mineral hematite. The metal in the mineral acts as an "acceptor," or dumping point, for thousands of trillions of electrons per square centimeter shuttled by the OmcA-donor. The function is a relic of respiration, in which the cell depends on the protein to dump electrons to maintain a steady flow of energy and prevent the organism-damaging accumulation of electrons.
PNNL staff scientist and co-author Uljana Mayer devised new tagging methods that enabled the team to isolate sufficient amounts of protein. The tags also allowed fast measurements of protein-mineral binding.
The researchers supplied the protein with energy--directly as electrons or in the form of a natural cellular fuel called NADH--and only during binding detected charge-transfer from protein to mineral, through a combination of techniques that included FCS, or fluorescent correlation spectroscopy, and confocal microscopy. These yielded a "fluorescence intensity trace" whose brightness depended entirely on whether hematite was available to bind with OmcA in solution. No hematite, dim; hematite, bright.
"The peak current, or flux, doesn't run long, just a few seconds," Squier said, "but flux is at least as good as what you would find in the most efficient bioreactors, which rely on living bacteria."
Biological fuel cells, or biofuel cells, are not yet powerful enough to be commercially viable but they offer the promise of breaking down sewage and other biological waste while generating electricity directly from the same process. An example, Squier said, is a self-powering sewage treatment plant.
Using pure protein opens up the possibility of shrinking biofuel cells to power small electronic devices, Squier said. Whole-organism biofuel cells require engineers to design a space-adding membrane that prevents unwanted reactions between fuel, the charge-transporting agent and the electron-accepting metal, the latter being the electrode that carries the electricity to the device. In purified protein fuel cells, the seal made by the protein coating on the electrode effectively acts in place of the membrane.
Bill Cannon | EurekAlert!
Cancer diagnosis: no more needles?
25.05.2018 | Christian-Albrechts-Universität zu Kiel
Less is more? Gene switch for healthy aging found
25.05.2018 | Leibniz-Institut für Alternsforschung - Fritz-Lipmann-Institut e.V. (FLI)
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences