SCIENCE & TECHNOLOGY CONCENTRATES
SMALL MOLECULE FOUND IN CONE SNAIL ARSENAL
Protein-mimicking molecules called peptoids can take on a never-before-seen secondary structure when they form, researchers report. “We’re interested in making synthetic versions of nature’s strucIn a peptoid tures,” says team leader Stenanosheet phen Whitelam of Lawrence formed from nearBerkeley National Laboratory. linear sigma strands, the “We found an interesting nano- blue and red ribbons show the material that formed through alternating twists of the sigma strand; a rule that nature doesn’t use.” gray = peptoid backbones, aqua and magenta = ionic side chains, yellow = aromatic side chains. Whitelam, Ranjan V. Mannige, and coworkers used molecular dynamics simulations to show that peptoid nanosheets are built from a zigzag structure they call a sigma (Σ) strand (Nature 2015, DOI: 10.1038/ nature15363). Protein backbones usually twist in only one direction, which leads to the familiar α helices and β strands. In peptoid backbones, in contrast, adjoining monomers twist in opposite directions, rendering the strand approximately linear. The Σ strands assemble into an extended twodimensional structure. The proposed structure is consistent with atomic force microscopy and powder X-ray diffraction measurements of the peptoid nanosheets. The researchers predict that with proper choice of sidechain interactions other secondary structure motifs should be possible that can be used to design three-dimensional nanostructures.—CHA
SiNN ligand and pinacolborane to make an alkynylboronate. Now they report that they can take the reaction a step further and add two more pinacolborane groups to produce triborylalkenes (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201507372). The second step is new, Ozerov says, in that diboration of a triple bond is accomplished not by insertion of the alkyne triple bond into a B–B bond, but rather by a second dehydrogenative process involving two B–H bonds. The other thing that is “strange” in this second step, Ozerov adds, is that it requires a different catalyst, but that catalyst
IRIDIUM DOUBLE CLUTCH PRODUCES TRIBORYLALKENES Tetrasubstituted olefins are important structural motifs in drugs and functional materials. Chemists have many ways to make them, including using polyborylated O H + HB
R
Ir catalyst
R
Bpin
Add CO
O
R
Bpin
pinB
Bpin
Alkynylboronate
Alkyne
Triborylalkene
HBpin
alkenes as intermediates. In exploring alternative routes to the borylated compounds, Oleg V. Ozerov of Texas A&M University and his colleagues previously reported the first example of dehydrogenative borylation of terminal alkynes, in which they used an iridium catalyst with a polydentate
can be made directly from the first one. The researchers found they could easily change gears in route by blanketing the reaction with carbon monoxide, which adds CO ligands to the original catalyst. With new triborylalkenes in hand, the team next plans to explore what they can do with them.—SR CEN.ACS.ORG
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PARASITIC PLANT’S FLEXIBLE NOSE
USDA/WIKIMEDIA COMMONS
Just before engulfing a tasty meal of a fish or a marine worm, a cone snail paralyzes its prey by injecting it with venom from a harpoonlike tooth. Scientists previously identified the paralyzing compounds in cone snail venom as polypeptides. O Some of them have even been N developed into pain medHN ication for people, such N H2N N as the synthetic injectable drug ziconotide (Prialt). Researchers led by UniO versity of Utah biologist HO Baldomero M. Olivera and Genuanine chemist Eric W. Schmidt now report that polypeptides aren’t the only paralyzing compounds in cone snail venom. They identified a small molecule in two different cone snail species—Conus genuanus and Conus geographus—that causes paralysis in mice when given at nanomolar doses (Org. Lett. 2015, DOI: 10.1021/acs.orglett.5b02389). Olivera and Schmidt’s team determined the compound’s structure and named it genuanine. Genuanine is a guanine derivative and the first small-molecule paralytic to be identified in cone snail venom. The researchers aren’t certain if genuanine is synthesized by the cone snail or its associated bacteria. Nevertheless, they say “it appears that small molecules are important and previously unrecognized contributors to the toxicity of cone snail venom.”—BH
RANJAN MANNIGE
PEPTOIDS DO A DOUBLE TWIST
Purple witchweed is a nefarious predator in Africa. Each year the parasitic plant devours billions of dollars’ worth of rice, sorghum, millet, and sugarcane crops by sniffing out chemicals released into the soil by the unsuspecting crops. These chemicals—a family of diverse hormones called strigolactones—are produced by many plants to recruit symbiotic root fungi. The strigolactones also activate germination of purple witchweed seeds, and the resulting parasitic seedOH
O
H
O
O
O
H Strigol, a strigolactone
Purple witchweed is a brutal parasite that sniffs out strigolactones, such as strigol, produced by its plant prey.
O
SCIENCE & TECHNOLOGY CONCENTRATES
lings rob their prey of nutrients. Researcha variety of digestion and metabolism ers have wondered how purple witchweed problems as well as cancer and Alzheimer’s can sniff out a variety of plants when they disease. Although researchers suspect the don’t all employ the same strigolactones. slowing down of an aging person’s biologiA team led by the University of Toronto’s cal clock has many causes, there might be Peter McCourt has the answer: Using X-ray a simple solution: dietary supplements. A crystallography, the researchers found that team of scientists led by Gad Asher at the the parasite’s strigolactone receptor bindWeizmann Institute of Science, in Israel, ing pocket is much larger than that found discovered that polyamines such as sperin other plants’ strigolactone receptors, midine found in foods including soybeans, takes about five hours. Chiu and his colincluding that of Arabidopsis green peas, and blue leagues are now working to develop methH plants, which are often used cheese can help reods that cut this time in half. “It’s an ambiN NH H2N 2 as a model plant (Science store normal circadian tious goal,” he tells C&EN. “Ambitious, but 2015, DOI: 10.1126/science. rhythms in aging mice feasible.”—MD Spermidine aac9476). The bigger binding (Cell Metab. 2015, DOI: pocket widens the range of strigolactones 10.1016/j.cmet.2015.09.011). The team deINDIUM TAKES AN purple witchweed can detect and thus extermined that polyamine levels in elderly pands its range of possible prey. The work mice drop at the same time their circadian ATMOSPHERIC could provide inspiration for those developclocks start slowing down. Feeding animals DOWNTURN ing strategies to curb the plant parasite.—SE the supplement restored their circadian clocks to the timing of younger mice. If Indium is widely used in electronics and the work extends to humans—and the reenergy technologies—for example, transMASS SPEC METHOD searchers caution that this has not yet been parent and conductive films of indium established—supplementing with polytin oxide are used in televisions and other FOR SAFER PUFFER FISH amines could help keep biological clocks electronic displays. As use of indium has People who eat puffer fish—also known as running on time.—SE grown, so too have concerns about its pofugu—take their lives in their own hands. tential toxicity and environmental fate. At These fish contain tetrodotoxin, a powerleast so far, however, it appears that older NANOPORE SENSORS ful neurotoxin that can spoil a good meal industrial processes released more indium and even kill the diner. The edible portions into the atmosphere than modern ones, ID VIRUSES IN A JIFFY of the fish vary by species, and some speaccording to a study of a bog in Massacies aren’t edible at all because the toxin is Researchers led by Charles Y. Chiu at the chusetts (Environ. Sci. Technol. 2015, DOI: too widespread. Because of the potential University of California, San Francisco, 10.1021/acs.est.5b03182). MIT researchers danger, Japanese law requires that puffer have used nanopore DNA sequencers to Sarah Jane O. White, Carrie Keach, and fish be labeled by species. And in the U.S., detect a range of viral infections directly Harold F. Hemond extracted a core sample only one species of puffer fish is legal. In an from clinical samples for the first time from Gowing’s Swamp, a wetland noted effort to improve food safety, researchers (Genome Med. 2015, DOI: 10.1186/s13073by philosopher Henry D. Thoreau in his at the National Research Institute of Police 015-0220-9). Using software developed famous journal about Walden Pond and its Science, in Kashiwa, Japan, developed a by Chiu’s team, the sequencers environs. They liquid chromatography/mass spectrometry identified Ebola, chikungunya, sliced the core, Year Indium, ng/cm2/year method to genotype 12 puffer fish species and hepatitis C viruses in human dated the slices 0.15 1872 (J. Agric. Food Chem. 2015, DOI: 10.1021/ samples in a matter of minutes. The using radioiso0.59 1894 acs.jafc.5b03703). Hajime Miyaguchi and approach can be used to detect any tope techniques, 1926 0.4 coworkers used the polymerase chain reacvirus on the basis of its distinct DNA and analyzed 1.15 1951 tion to amplify specific sequences from the sequence, Chiu says. The team used them for indium 1.54 1976 mitochondrial genes for each species’ 16S MinION sequencing devices, which and other metals. 2000 0.14 ribosomal RNA. They then digested the amare developed by the company OxThey found that plified DNA and analyzed it with high-resoford Nanopore Technologies. These indium deposilution LC/MS. The researchers were able to small USB devices record electronic signals tion started rising in the late 1800s and distinguish all species, except for two puffer as DNA threads through pores created peaked around 1970, when the U.S. implefish that have the same sequence.—CHA by membrane-bound proteins in a chip. mented stricter controls on particulate The nanopore platform interprets these emissions to the atmosphere by activities signals to reveal a DNA molecule’s unique such as coal combustion and metal smeltDIETARY SUPPLEMENTS sequence. The platform’s portability and ing. Since then, indium concentrations in the bog have dropped significantly. The COULD KEEP BIOLOGICAL real-time analysis capabilities make it attractive for point-of-care screening, but study suggests that release of indium to the CLOCKS ON TIME Chiu says there are obstacles to overcome atmosphere by current electronics manuAs we age, our circadian rhythms tend to before the technology can be widely used facturing and product disposal is considerfall out of sync with the normal 24-hour in the clinic. For instance, despite the short ably lower than historical sources in North day. This dysregulation is associated with sequencing time, preparing a sample still America.—JK CEN.ACS.ORG
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OCTOBER 12, 2015
OXFORD NANOPORE
MinION devices are roughly the size of USB memory sticks.
