SCIENCE & TECHNOLOGY CONCENTRATES
TRANSGENIC SILKWORMS MAKE FLUORESCENT SILK Silk’s strength and biocompatibility make the fiber as attractive in biomedical applications as it is in consumer textiles. But the worms that produce the best silk in the largest quantities resist genetic engineering by becoming dormant, a process called diapause, when exposed to gene transfer agents. For that reason, mass-produced transgenic silk has been out of reach. Toshiki Tamura of Japan’s National Silk produced by transgenic silkworms was used to make this doll-sized wedding dress.
Researchers who want to combine tiny volumes of liquid have few simple options when it comes to mixing for lab-on-a-chip applications or microliter bioassays. Passive diffusion is slow, and violent stirring can break droplets apart instead of mixing them together. Thanks to a team in Singapore, researchers can now reach for the world’s smallest magnetic stir bars. At just 17 µm long and 75 nm to 1.4 µm thick, these super small stir bars can mix as little as 4 pL of liquid (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201303249). A team at Nanyang Technological University led by Hongyu Chen created the stir bars from oleic acid-stabilized Fe3O4 nanoparticles that are 40 nm in diameter. They modified the nanoparticles with citric acid to render them water-soluble and dissolved them. The team then used a magnet to align the nanoparticles and gave them a silica The world’s smallest stir bars, as coating to ensure they stayed straight and seen with a transmission electron microscope. rigid. They centrifuged the mixture to purify the stir bars, which they dispersed in solutions of various concentrations for stirring. While VIDEO ONLINE stirring, the nanosized stir bars remain suspended in solution indefinitely. And removing them is as simple as placing a stationary magnet beneath the droplet and letting the stir bars settle out of solution over the course of about five minutes.—BH ANGEW. CHEM . I NT. ED.
Making an electron-transfer protein more flexible can help it conduct electrons more readily. This finding could help researchers improve the efficiency of energy-conversion processes such as photosynthesis and respiration. A theory developed by Rudolph A. Marcus of Caltech, for which he won the 1992 Nobel Prize in Chemistry, states that lowering a protein’s reorganization energy—the energy required to rearrange a protein’s internal structure during electron transfers—makes such transfers speedier. The rational design of protein electrontransfer centers to lower reorganization energies has rarely been demonstrated. Now, Yi Lu of the University of Illinois, Urbana-Champaign, and coworkers show that engineering the electron-transfer protein azurin by modifying hydrophobicity or hydrogen-bonding of residues around the protein’s copper center makes the residues interact with one another more flexibly, lowering the protein’s reorganization energy and improving its electron-transfer efficiency (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1215081110). The findings could lead to “a deeper understanding of electron transfer in other systems and the de novo design of electron-transfer proteins for applications such as advanced energy conversion,” Lu says.—SB
A STIRRING ADVANCE
Institute of Agrobiological Sciences and coworkers have now gotten around the problem by mating nondiapausing silkworms modified to produce fluorescent silk with diapausing varieties (Adv. Funct. Mater. 2013, DOI: 10.1002/adfm.201300365). The resulting offspring produce silks in large quantities that fluoresce green, orange, or red and have 80 to 90% of the strength of commercial silk. The group also developed gentle ways to process the silkworms’ cocoons into usable fiber to avoid denaturing the florescent proteins. The team says this combination of modern and traditional genetic manipulation could allow farmers to produce “functional silks possessing protein sequences that confer unique biological activity” and serve as catalysts or therapeutics.—CB ADV. FUNCT. MATER.
TWEAKED PROTEIN CONDUCTS ELECTRONS FASTER
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PROBING RADIOACTIVE CESIUM BINDING TO SOIL When radioactive cesium is deposited in soil, such as during the 2011 Fukushima Daiichi nuclear disaster in Japan, remediation is difficult. 137Cs has a half-life of 30 years and cannot be easily removed from soil by standard washing with water or acid solutions. A group led by Kiminori Sato of Japan’s Tokyo Gakugei University examined clay minerals treated with a CsCl solution to determine how cesium binds to the materials, reasoning that a better understanding of the process may lead to improved soil remediation methods (J. Phys. Chem. C 2013, DOI: 10.1021/jp403899w). They found that cesium binds tightly in locations where mineral layers insert (intercalate) between two others, creating wedge-shaped open spaces. Where one mineral layer intercalates, the team found Cs+. Where two layers intercalate, the team found Cs2O and CsOH as well as Cs+. The researchers propose that at double-intercalation sites, Cs+ binds to the layer surfaces and also adsorbs strongly
SUPERMARKET PRODUCE TRACKS TIME Cabbage, spinach, sweet potatoes, carrots, and other types of produce can respond to the rise and fall of the sun for up to a week after harvest. The ability to track time through cellular circadian clocks has profound implications for the nutritional value of produce and its ability to withstand herbivores, notes a team of plant biochemists led by Janet Braam of Rice University (Curr. Biol. 2013, DOI: 10.1016/j.cub.2013.05.034). The change in light that occurs at sunrise OH O HO HO
O S
S CH3
OH
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GOODSPEED ET AL.
4-Methylsulfinylbutyl glucosinolate
cues plant cells to produce useful phytochemicals. These compounds, including 4-methylsulfinylbutyl glucosinolate, are produced at dawn to deter foraging by insect herbivores that normally feed at that time. Produce stored or transported in constant dark or light conditions may not generate enough of the protective compounds, making “the crop more susceptible to herbivory,” the team notes. Furthermore, continued production of 4-methylsulfinylbutyl glucosinolate is desirable because the compound has anticancer properties. The produce industry may want to synchronize light levels with the sun’s 24-hour cycle to improve the lifetime and nutritional value of produce, the researchers suggest.—SE
PLASTIC WASTE HOSTS MICROBIAL ARRAY A surprising suite of microbial species colonizes plastic floating in the ocean and may speed the waste’s breakdown, according to a study (Environ. Sci. Technol. 2013, DOI: 10.1021/es401288x). Researchers, led by Lin-
da A. Amaral-Zettler at the Marine Biological Laboratory and Tracy J. Mincer at Woods Hole Oceanographic Institution, analyzed plastic samples collected from the Atlantic Ocean. A centimeter-sized sample contained hundreds of microbial species distinct from those found in surrounding waters. Scanning electron micrographs show the bacteria lodged inside pits in the plastic. The team thinks that the bacteria eat into the polymers, weakening the pieces and possibly causing them to break down more quickly. Supporting this hypothesis, some of the plastic-burrowing bacteria are closely related to species known to consume other types of hydrocarbons, such as oil. Because plastic waste poses health risks to marine life, it would be promising to understand how microbes may break down plastics, says Michael Cunliffe of the Marine Biological Association of the U.K. But the process “needs to be shown in a bit more detail.”—JNC
Bacteria (spheres) occupy pits in plastic waste found in the ocean.
sites for complexing with partners. They were tagged with fluorescent agents to monitor E1A folding, which would vary depending on the system’s cooperativity. Over a broad range of concentrations of the two binding partners, the population of various protein complexes changed. They observed changes in the binding cooperativity sign and magnitude, depending on the availability of E1A binding sites. The researchers propose that such effects may be a common control mechanism in protein networks.—CHA
NANOTUBE ELECTRODES SPEAR NERVE CELLS To better understand how the brain works, neuroscientists plunge fine-tipped electrodes inside nerve cells to measure the electrical signals they transmit. Oftentimes, researchers use glass-encased electrodes called micropipettes, but the probes can be brittle, making them difficult to work with. Metal electrodes have been tried, too, but it’s difficult to sharpen their tips sufficiently to poke them into cells. For a more robust alternative, researchers PLOS ONE
to the edges of the inserted layers by reacting with oxygen along the edges, forming Cs2O. Cs2O may further react with water to form CsOH.—JK
ERIK ZETTLER/SEA EDUCATION ASSOCIATION
SCIENCE & TECHNOLOGY CONCENTRATES
PROTEIN DISORDER FLIPS SWITCH The binding of one molecule to a protein can affect subsequent binding of another molecule. That molecular response is known as allostery. Scientists already knew that intrinsic protein disorder—the lack of a defined structure—can modulate allosteric effects such as cooperativity. In positive cooperativity, binding of a molecule at one site increases binding of another molecule at a different site. Negative cooperativity decreases binding of the second molecule. Ashok A. Deniz, Peter E. Wright, and coworkers at Scripps Research Institute, La Jolla, Calif., now show that an intrinsically disordered protein and its binding partners can switch between positive and negative cooperativity (Nature 2013, DOI: 10.1038/nature12294). The researchers examined systems consisting of truncated versions of the intrinsically disordered protein E1A and two of its binding partners. The E1A constructs offer different CEN.ACS.ORG
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At the tip of an electrode made of carbon nanotubes, one tube (arrow) sticks out.
at Duke University, led by Bruce R. Donald and Richard Mooney, have developed ultrafine electrodes made of carbon nanotubes for nerve cell recording (PLoS One 2013, DOI: 10.1371/journal.pone.0065715). “With carbon nanotubes, we can make something very strong and conductive that is pointy like a harpoon,” Donald says. To make the 1- to 2-mm-long spears, the Duke researchers used dielectrophoresis to draw nanotubes out from the end of a tungsten wire, and they stiffened the whole assembly by running current through it. Then they coated the electrode with an insulating compound and etched its tip with a focused ion beam. Using the new electrodes, the team successfully recorded signals from inside single nerve cells in slices of mouse brain and from outside nerve cells in the brains of live mice.—LKW
