This year, Roderick MacKinnon was recognized for working out the atomic structure of an ion channel and Peter Agre for discovering that a major protein found in red blood cells functions primarily as a water channel. Agre went on to establish the family of related channels, which he named "aquaporins." Solving the structure of these channels provided a platform for exploring the underlying molecular mechanisms that allow the proteins to function as filters and maintain osmotic equilibrium. Robert Stroud and colleagues, as reported in this issue of PLoS Biology, have now solved the structure of the water channel from Escherichia coli called aquaporin Z. This channel is especially interesting in that it selectively conducts only water at high rates.
Aquaporins form a large, diverse family of proteins and have been found in bacteria, plants, and animals. Less than a decade ago, scientists discovered the aquaporin Z gene (aqpZ) in E. coli, pointing to the protein’s role in regulating water transport in this prokaryote. The aquaporin Z channel protein in E. coli can accommodate a flow of water at rates six times higher than GlpF (aquaglyceroporin glycerol facilitator, a channel protein that transports both glycerol and water in E. coli) making it the prime subject for studying the selectivity of a high-conducting water channel. And because the two main classes of aquaporins occur in E. coli--which means they’re exposed to the same cellular environment--the opportunities for comparative structural and functional analyses, combined with site-directed mutagenesis, promise to provide valuable insights into the molecular underpinnings of the selectivity of functionally different aquaporins.
After producing a recombinant form of AqpZ in E. coli, the proteins were crystallized--capturing five water molecules inside--and then analyzed by state-of-the-art high-resolution X-ray diffraction techniques. The architecture of aquaporin Z is typical of aquaporins, with a spiral of eight oxygens providing water-binding sites inside the channel. The outer membrane and cytoplasmic ends of the channel are wider than the interior, which is long and narrow. This structure demonstrates that aquaporin selectivity arises in part from erecting a physical barrier: small molecules, like water, can easily pass, but larger ones simply can’t fit. And the strategic positioning of amino acid residues with hydrophilic or hydrophobic properties along the channel helps police the influx of molecules based on their affinity for water. While it seems two amino acid chains located in the middle of the channel also provide a water-friendly surface, Stroud et al. say they play a more intriguing role. Noting that the water molecules occupy the channel in single file, the scientists explain that such an orientation would normally facilitate the random flow of protons (or hydrogen ions), which would be lethal to the cell. This central amino acid pair, they say, restricts the behavior of water molecules in the center of the channel in such a way that prevents "proton jumping" yet keeps the water flowing. With two structural models of aquaporins down to the atomic level in the same species, scientists can now begin to investigate the molecular mechanisms that facilitate their selectivity. The importance of understanding these widely distributed channel proteins was underscored by the Nobel awards this year.
Philip Bernstein | PLoS
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