Research

A Transporter ABCG40 Mediates Cellular Uptake of the ABA, the Drought Resistance Hormone (2010.1.19)

Professor Youngsook Lee (Division of Integrative Biology and Biotechnology) and her team have found a transporter carrying abscisic acid (ABA), a stress hormone, synthesized in plants undergoing stresses like extreme climate or salinity. Their results integrate ABA dependent signaling and transport processes, and it is expected to open a new venture for the engineering of drought-tolerant plants. They have succeeded to find the existence of transporter ABCG40 that can transport ABA, a hormone known to be produced in responses to environmental stress such as extreme temperatures, high salinity, or drought and plant pathogens. In both animals and plants, hormones are known to play essential roles in the regulation of growth, development, and environmental response, and they are circulated throughout the organism in part by the extracellular fluid. Plant hormones are known to be transported over long distances, such as auxin and ABA. These two are weak acids, and thus, they exist in either protonated, uncharged or in anionic forms depending on the prevailing pH. In drought condition, the pH of plant extracellular fluid increase. Therefore, for effective transportation of anionic forms ABA into the cells, plant needs protein carriers. For ABA to be able to protect a plant, it should be imported inside of the plant cell, but no transporter has been identified before. The ABCG40 proteins that absorb ABA quickly into cells, and it activates stress-tolerant genes inside cells. Drought-stress experiments provided further evidence that AtABCG40 is integral to stress tolerance. Plants were grown for 2 weeks under standard conditions, and water is subsequently withheld. Leaves of the two mutant lines (abcg40-1, abcg40-2) withered faster than those of the wild-type (WT) plants (see figure A). Stomata of abcg40 plants are less sensitive to ABA. In figure B, the delayed elevation of leaf temperature after ABA treatment of abcg40 plants was compared with wild-type (WT). Leaf temperature was monitored using an Infrared Thermal Imaging Camera. Considering the fact that the rapid adjustment to a stress, such as drought stress, is a prerequisite for plant survival, these results have significant potential to further applications. “This finding of uptake process of ABA and the crucial role of the transporter ACBG40 may help develop a plant that is adaptable to the extreme conditions of environmental stresses,” Professor Lee commented. Professor Enrico Martinoia, a renowned professor in the field of plant ABC transporters from Switzerland, has participated in this research. The results are published on the January 18 issue of Proceedings of National Academy of Science of USA (PNAS). This research is supported by the Ministry of Education, Science and Technology, and National Research Foundation of Korea.

Mussel Adhesive Protein with Improved Property Developed (2010.3.4)

Professor Hyung Joon Cha (Department of Chemical Engineering) and his team have succeeded in developing a highly condensed liquid bio-adhesive material based on the mussel adhesive proteins (MAPs) by complex coacervation, which shows superior adhesive properties. Recently, MAPs found in byssus of mussel, have come to be recognized as useful biomaterials for direct use as bio-adhesives in medical applications and in the engineering of new marine-inspired adhesive materials. As purified natural MAPs are difficult to obtain, it has not been possible to experimentally validate the complex coacervation model from mussel, which make the results more valuable and remarkable. Professor Cha’s team has used the characteristics of mussels that grow attached on boulders as secreting adhesive proteins. Byssus is composed of byssal thread and plaque in edges. MAPs exhibit both non-toxicity and strong attachment to any type of inorganic or organic surface in a wet environment. Various type of MAPs has been defined by fp, abbreviation for foot protein, and types 1 (fp-1), 3 (fp-3), and 5 (fp-5) MAPs have been extensively studied. However, the details of the adhesion process, including condensation of MAPs in vacuoles, and secretion as a watery liquid but with no dispersion into the surrounding water, have remained poorly understood. The team has already been able to solve the problem of getting the materials by complex coacervation. In the present study, the team investigated the formation of complex coacervates using hybrid MAPs (fp-151 and fp-131) and hyaluronic acid (HA). A coacervate is a tiny spherical droplet of assorted oppositely charged polymers which are held together by electrostatic interaction. Complex coacervation refers to the phase separation of a liquid precipitate when solutions of two hydrophilic colloids are mixed under suitable conditions. HA is an anionic polysaccharide that contributes to cell production and migration as one of the major components of the extracellular matrix, and is found in all tissues and body fluids of vertebrates, as well as in some bacteria. In addition to those, microencapsulation of oil particles was performed using complex coacervation to demonstrate potential application in the field of adhesive drug carriers. This microencapsulation system could be effectively used in the development of new adhesive biomaterials. It includes self-adhesive microencapsulated drug carriers for biotechnological and biomedical applications such as bio-cosmetic products and food additives. “Through this research, we have developed a bio-adhesive material with extraordinary physical characteristics, and it is significant that we have found the mechanism of mussels’ secretion of concentrated adhesive substance. We believe this has opened various possibilities of utilization of bio-adhesive materials,” commented Professor Cha. The results of the study were published in the March 1, 2010, online issue of Biomaterials, the May issue of the journal Biomaterials. This work is supported by the National Research Laboratory program and the Brain Korea 21 program from the Ministry of Education, Science and Technology, Korea.

Water Repellent Surface Now Available for Wider Variety of Industrial Applications (2009.10.14)

Professor Kijung Yong (Department of Chemical Engineering) and his group have succeeded in developing an original technology utilizing the lotus effect, which may be used toward development of a variety of applications using coated surfaces. Leaves of the lotus flower have very high water repellency due to the complex, nanoscopic structure of their surface. Superhydrophobic nanostructured surfaces, such as the lotus leaf, have shown potential for a variety of applications, including microfluidics in biotechnology, fog-resistant coatings, impermeable textiles, anti-contamination, and self-cleaning surfaces. Nanostructures with low surface energies reduce the contact area of water droplets and prevent the penetration of water into spaces between nanoposts of aligned nanostructures under static conditions. However, superhydrophobicity must be maintained under dynamic rather than stationary droplet conditions for practical applications. Professor Yong and his group conducted a study of the effects of dynamic impacts on tungsten oxide nanostructures having different surface energies due to the adsorption of self assembled monolayers (SAMs) with various alkyl chain lengths. The team also investigated the effects of ultraviolet (UV) irradiation on chemically modified tungsten oxide nanowire arrays, where the photodecomposition of SAMs caused changes in surface energies and the behavior of impinging droplets. Through the research, three states of wetting - wetting, partial wetting, and bouncing states - were identified through the balance between anti-wetting and wetting pressures, opening up the way for establishment of technology for designing water-repellent surfaces for impinging droplets. Professor Yong’s group made a change in the characteristics of a surface through two separate methods: by the bottom-up way which synthesizes nano-waves, and by the top-down which exposes the synthesized nano-waves to ultra-violet rays. Using a high-speed camera to monitor the variation of a water droplet’s dynamic behavior depending on different surface energies, the technology was demonstrated suitable for water-dropping daily conditions. The results of the study were introduced as the cover paper in the October 12, 2009, online issue of Applied Physics Letters (2009, vol. 95, issue 15).

Bridge between Consciousness and Unconsciousness Identified (2009.11.30)

Despite its potential risks, general anesthesia and how it leads human brain to unconsciousness is still not known. A POSTECH research group has been investigating the nature of consciousness as well as control of the level of consciousness through anesthesia, whose effort has drawn much attention of the academia. Professor Seunghwan Kim (Department of Physics) and his team, in a joint study with POSTECH graduate Doctor UnCheol Lee of University of Michigan and a Seoul Asan Medical Center team, have presented evidence that the transition from consciousness to unconsciousness occurs by the suppression of the information flow channel in the brain through experimentation with general anesthesia. The research group derived general anesthesia from injecting propofol into normal people and measured the amount and the direction of information flow both in the frontal lobe, which takes charge of recognition, and in the occipital lobe, which processes sensory information. The result was that the information flow from the frontal lobe toward the occipital lobe decreases at the same time the patient becomes unconscious but the flow in the opposite direction keeps uniform at all times. This indicates that the information processing which deals with senses from the outside before unconsciousness is performed constantly in the patient’s brain under the general anesthetic state, but the information processing after unconsciousness is strongly suppressed. Also, this result is expected to be applied to a new index development to prevent accidents such as awakening during surgery. “Through our research, we have found the clue to solve the many puzzles of consciousness, such as the transitional process from consciousness to unconsciousness,” said Professor Kim. The team also identified that each individual has his/her own distinctive patterns in brain activity, both in conscious and unconscious states. This provides scientific proof for the fact that there exist individual differences in emotional reaction to the same situation such as watching the same movie or experiencing the same social and environmental circumstances. The world-renowned anesthetist Anthony Hudetz of the University of Wisconsin remarked, in the commentary for the POSTECH team’s research, that the findings of the study “opened up a new door to the neurological understanding of anesthesia and consciousness.” The results are expected to contribute to the investigation of the existence and role of the peculiar information flow system in not only the unconscious but also many forms of the conscious state including brain dead, vegetative, sleeping and epileptic. The findings were introduced as the Target Paper in Consciousness and Cognition, Volume 18, Issue 4 (1069-1078).

A Spoonful of Sugar Makes Life Span Go Down (2009.11.4)

Many studies have addressed the effect of sugar in the diet on obesity and diabetes. Professor Seung-Jae Lee (Division of IT Convergence Engineering, Department of Life Science, School of Interdisciplinary Bioscience and Bioengineering) and his group report that it might also be taking years off the life span. Professor Lee’s group, in collaboration with Professor Cynthia Kenyon of the University of California, San Francisco, discovered that glucose inhibits the activities of the glycerol channel in C. elegans, shortening the life span of the worm by about 20 percent. The group traces the effect to insulin signals, which can block other life-extending molecular players. Insulin reduces similar glycerol channels in mammals, suggesting that this glucose-responsive pathway might be conserved evolutionarily. The findings raise the possibility that a low-sugar diet might have beneficial effects on life span in higher organisms. The research group discovered in the early 90s that mutations that effected insulin signals could double the normal life span of worms. Specifically, a mutation in a gene known as daf-2 slowed aging and doubled life span. That longer life needed other genes called the FOXO transcription factor DAF-16 and the heat shock factor HSF-1. Now, the researchers show that those same genes are also involved in numbering the days of worms which are fed on glucose. In fact, glucose makes no difference to the life span of worms that lack DAF-16 or HSF-1, they show. Glucose also completely prevents the life-extending benefits that would otherwise come with mutations in the daf-2 gene. Ultimately, worms fed a steady diet containing glucose show a reduction in aquaporin channels that transport glycerol, one of the ingredients in the process by which the body produces its own glucose: if there is not enough glucose, the body makes it with glycerol. That glycerol has to first get where it needs to go, which it does via the aquaporin channels. Further studies are needed to see if these same effects of sugar can be seen in mice, or even people. But there is reason to think they may. “Although the mechanism by which glucose shortens the life span of C. elegans is not yet fully understood, the fact that the two mammalian aquaporin glycerol-transporting channels are downregulated by insulin raises the possibility that glucose may have a life-span-shortening effect in humans, and, conversely, that a diet with a low glycemic index may extend human life span,” the researchers wrote. The findings may also have implications for drugs in development for the treatment of diabetes, which are meant to block glucose production by inhibiting glycerol channels. The new findings suggest that glycerol channels might be doing something else, and that drugs designed to block them might have a downside. The results of the study were introduced under the title, “Glucose Shortens the Life Span of C. elegans by Downregulating DAF-16/FOXO Activity and Aquaporin Gene Expression” in the November 4, 2009, issue of Cell Metabolism, Volume 10, Issue 5, Pages 379-391.

Eco-Friendly Ultrahigh-Density Data Storage Material Developed (2009.10.7)

Professor Jin Kon Kim (Department of Chemical Engineering) and his group have succeeded in developing macromolecule materials which use pressure to store terabit-scale ultrahigh-density data at room temperature, as well as the supporting technology to write, read, and erase the ultrahighdensity array of nanoscopic indentations. The existing technology for fabricating nanopatterns, developed by IBM, was based on a thermomechanical recording system, using a heated atomic force microscope (AFM) tip at about 350°C. However, in addition to the difficulties in the fabrication of heated AFM tips, a relatively large power was consumed because of the very small percentage (<1%) of heat transmitted from the heated AFM tips to the polymer film. Professor Kim’s group introduced a novel concept of using AFM, but without a heated tip. The nanopatterns are generated on the polymer film by the AFM tip at room temperature, and these nanopatterns retain their original shapes at room temperature. This process is only possible by using a specific block copolymer film exhibiting a baroplastic property that enables processing at a relatively low pressure and temperature by micro-phase transition. The team found that polystyrene-block-poly(n-pentyl methacrylate) copolymer (PS-b-PnPMA) exhibits baroplasticity properties, and that because of its sensitive transitions to hydrostatic pressure, the microdomain PS-b-PnPMA disappears and becomes disordered at the relatively low pressure. By simple indentation with the AFM tip on the PS-b-PnPMA film at room temperature, a nanopattern was generated. An ultrahigh areal density of up to 1.03Tb in-2 was achieved, and this value could be increased further if a more sharpened AFM tip is available. The research group also demonstrated that the generated nanopatterns could be transformed into electric signals using a piezoelectric sensing method. Furthermore, local and bulk erasing of the nanopatterns was successfully carried out, and repeated erasing and rewriting processes up to 10 cycles were also demonstrated without any damage to the film. This newly generated pressure-based phase-change memory at room temperature may expedite the development of a next-generation ultrahigh-density data storage medium. The technology is particularly expected to save energy consumption compared to the existing technology of IBM, whose operation requires a temperature of about 350°C. “Now, we can construct nanoscale patterns using only pressure at room temperature. Our achievement has prepared a technology basis for development of very high scale data storage materials, for which many global enterprises are scrambling,” commented Professor Kim. The results of the study were published in the September 13, 2009, online issue of Nature Nanotechnology (2009, vol. 4, no. 11, 727-731) and introduced in News and Views of the same issue (703- 704). The work was also highlighted in NPG Asia Materials (2010, vol. 2, no. 1, 10).

Nanoscale Photonic Circuit Near Development (2009.5.25)

Professor Moon-Ho Jo (Department of Materials Science and Engineering) and his group, in a joint study with a Harvard University team, have materialized a new all-electrical surface plasmon polaritons (SPPs) detection technique based on the near-field coupling between guided plasmons and a nanowire field-effect transistor. Photonic circuits can be much faster than their electronic counterparts, but it is difficult to miniaturize them below the optical wavelength scale. Nanoscale photonic circuits based on SPPs are a promising solution to this problem because they can localize light below the diffraction limit. However, there is a general trade-off between the localization of an SPP and the efficiency with which it can be detected with conventional far-field optics. The new detectors developed by Professor Jo’s research group are both nanoscale and highly efficient (~0.1 electrons per plasmon), and a plasmonic gating effect can be used to amplify the signal even higher (up to 50 electrons per plasmon). The researchers used the technique to electrically detect the Plasmon emission from an individual colloidal quantum dot coupled to an SPP wavelength. These results may open up several directions for further research. New on-chip optical sensing applications may be enabled. The achievement also marks a key step towards ‘dark’ optoplasmonic nanocircuits in which SPPs can be generated, manipulated and detected without involving far-field radiation. The plasmon-detection sensitivity could be improved by using a nanoscale avalanche photodiode as the SPP detector, potentially enabling efficient electrical detection of individual plasmons. Electrical plasmon detectors could lead to new applications for optical sensing without collection optics, including the measurement of plasmon states in which coupling to the far-field is suppressed by symmetry. Finally, the strong near-field coupling between single-plasmon emitters and plasmonic nanocircuits could lead to completely new capabilities that are not available with conventional photonics, such as nonlinear switches, single-photon transistors and quantum non-demolition detectors. The study results were published in the May 24 online edition of Nature Physics. Professor Moon-Ho Jo Department of Materials Science and Engineering Tel: +82-54-279-2158 Fax: +82-54-279-2399 E-mail: mhjo@postech.ac.kr

Doughnut-Shaped Polymer Nano Structure Developed (2009.6.11)

Professor Taihyun Chang (Department of Chemistry) and his group have developed toroidal micelles of uniform size from diblock copolymers. Block copoloymers can spontaneously self-assemble in a selective solvent to form micelles of various morphologies such as spherical micelles, cylindrical micelles, and vesicles. Recently, the variety of micellar shapes have been expanded to unconventional forms including toroids, tubes, disks, helices, and other complex forms. Although the toroid-shaped micelles have been reported earlier, the applicability of the toroid structure had been low due to the difficulty in achieving uniformity in size despite the simplicity in shape. All the doughnut-shaped micelles reported to date were practically ring closure products of rodshaped micelles, thus their sizes are not uniform. Professor Chang’s team succeeded in developing pure toroidal micelles of high uniformity in shape and size using block copolymer with a block of low glass transition temperature in a selective solvent. The micelle can retain its doughnut-shaped structure and size in solution over several months, appearing to be a thermodynamically stable structure. The doughnutshaped micelle, realized utilizing the phenomenon of block copolymer self assembly, is stable enough to be used as a template to grow metal nanoparticles. The nanosized toroidal objects have great potential for practical applications. With the stable and well-defined structure, the doughnut-shaped micelles are expected to serve as a model system to study their properties, as well as being a promising candidate for a nanotemplate in the evolving field of nanoscience and nanotechnology. Professor Taihyun Chang Department of Chemistry Tel: +82-54-279-2109 Fax: +82-54-279-3399 E-mail: tc@postech.ac.kr

Korean Researchers Develop 'Nano-Lens' (2009.7.23)

A team of multinational scientists developed a technique to produce tiny, nano-sized optical lenses, a breakthrough that may open new possibilities in microscopy and bio-imaging, the researchers said Wednesday. In a study published in peer-review journal Nature, the researchers, led by Kwang Kim, a researcher from the Pohang University of Science and Technology (POSTECH), said they found that cup-shaped organic molecules, called calyx hydroquinone (CHQ), self-assemble into a lens shape when placed on a surface. The nano-lenses produced in this way could push lens-based magnification to resolve features beyond the limits of diffraction, or the bending of light waves around small obstacles and the spreading of waves past small openings, Kim said. Lens-based microscopes are constrained by the diffraction limit of light, which causes the final image to contain less information that what is present in the source. Nano-lenses developed by Kim and his colleagues deflect light in curbed beams, in contrast to conventional optical lenses, resulting in very short focal lengths. This allows them to resovle features beyond the diffraction limit, enabling features of the order of 200 nano-meters or smaller to be resolved, Kim said. "Such spherical nanolenses provide new pathways for lens-based near-field focusing and high-resolution optical imaging at very low intensities, which are useful for bio-imaging, near-field lithography, optical memory storage, light harvesting, spectral signal enhancing, and optical nano-sensing," the researchers said in the paper published in Nature. Kim's work was funded by the Ministry of Education, Science and Technology's "global research lab" project, and also participated by Columbia University's Philip Kim, Laura Kaufman and Wong Chee Wei.

H2 Adsorbing Synthetic Small-Pore Zeolite Discovered (2009.8.11)

Professor Suk Bong Hong (School of Environmental Science and Engineering) and his research group have discovered that PST-1 (POSTECH number 1), the newly named synthetic small-pore zeolite molecular structure, selectively adsorbs hydrogen. The zeolites’ ability to discriminate between molecules of different sizes and shapes has long been recognized. However, examples of selective adsorption of the smallest gases in zeolites are scarce. PST-1, the synthetic small-pore zeolite with the natrolite topology and a potassium gallosilicate composition, was discovered to adsorb only the smallest gases, thus allowing discrimination from slightly larger molecules, and furthermore, to be selective for hydrogen over helium, despite the smaller size of the latter. The research has been watched closely, because PST-1, which dehydrates easily at low temperature (60°C) and stably maintains its structure at high temperature (800°C), suggests the possibility of its utilization as the first selective separation material for the small gas molecules such as hydrogen and helium. The PST-1 zeolite is also expected to be used in effective discrimination of carbon dioxide, the primary greenhouse gas. The pre-existing method used for hydrogen separation requires a temperature above 300°C, or removes impurities rather than adsorb hydrogen, so the synthesis of PST-1 is expected to propel development of more economical and selective manufacturing process for high purity hydrogen, explained Professor Hong. An international patent application process is ongoing for the technology, with the anticipation that the high purity hydrogen production and carbon dioxide dissociation using the unique discriminative quality of PST-1 is to become pivotal technology in the environmental and energy industries. The research results were introduced in Angewandte Chemie Volume 48, Issue 36. Professor Suk Bong Hong School of Environmental Science and Engineering Tel: +82-54-279-2284 Fax: +82-54-279-8299 E-mail: sbhong@postech.ac.kr