NEWS OF THE WEEK
CHEMICAL BIOLOGY:
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have a more controllable cousin on the horizon. Researchers led by Dirk Trauner, a chemist at the University of Munich, have figured out the mechanism by which molecules with the ability to block voltage-gated ion channels can be turned on and off repeatedly by light. Because ion channels are at the foundation of hu-
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RUGS THAT ARE modulated by light could
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In the trans configuration, AAQ stems the flow of potassium in voltage-gated K+ channels. In the cis configuration, it allows the ion to flow.
Photosensitive reaction opens or shuts potassium’s flow
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man perception, these light-sensitive Cis ion channel blockers, also called photochromic ligands, could one day be used in light-controlled anesthesia or vision restoration, Trauner says. Light has long been used to activate drugs, leading to several successful so-called photodynamic therapies, such as those for treating cancer. More recently, Trauner and his colleagues have spearheaded an effort to turn on molecules that target biological proteins—and then
IRONING OUT MERCURY’S MAKEUP This false-color image taken by NASA’s Messenger spacecraft shows a billion-year-old volcanic doublering basin on the surface of Mercury.
PLANETARY SCIENCE: New results from spacecraft flyby show iron-rich surface
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HE SURFACE OF Mercury, believed to be curi-
ously deficient in iron even though the planet has an enormous iron core, might instead be rich in iron and titanium, according to new data collected by NASA’s Messenger spacecraft. The finding could force scientists to retool models of the planet’s formation and evolution. Scientists reported the first direct elemental abundance measurements of Mercury’s surface at a press conference on Nov. 3. Messenger captured the data with its neutron spectrometer during the craft’s third and final flyby of Mercury. In the coming months, Messenger will settle into orbit around the planet to begin mapping it in detail in 2011. The neutron spectrometer’s detection of WWW.CEN-ONLINE.ORG
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turn them off again—by means of light-activated cistrans isomerization. Early photochromic ligands could bind only to ion channels that had been genetically modified to permit attachment. Last year, Trauner and colleagues reported an azobenzene molecule dubbed AAQ that can photosensitize naturally occurring voltage-gated potassium channels in neurons (Nat. Methods 2008, 5, 331). Now the team is reporting AAQ’s mechanism of action, along with a whole family of related azobenzenes that can block voltage-gated potassium ion channels in a photo-controllable manner (Angew. Chem. Int. Ed., DOI: 10.1002/ange.200904504). In particular, the team finds that AAQ diffuses into brain cells and binds noncovalently in an area of the channel interior in which potassium ions would normally pass. In the trans configuration, AAQ blocks the channel, whereas in the cis configuration, it allows potassium ions to flow. N+ Given the similar structure, function, and pharmacology of voltage-gated ion channels, Trauner’s “beautiful” new study points to the possibility of creating photochromic ligands for other such channels, comments Stefan Herlitze, a neuroscientist at Case Western Reserve University. But unless the molecules are made selective for specific channels in specific cell types, their therapeutic potential will be limited, say other researchers, including biochemist Timothy Ryan of Cornell University. In as-yet-unpublished work, Trauner’s group has found that the molecules can be made more selective by chemically tweaking their hydrophobic tails.— SARAH EVERTS
an iron-rich surface contradicts other, less definitive data from Messenger’s first flyby two years ago (C&EN, July 28, 2008, page 65). Understanding how the new results affect theories about Mercury’s formation “will keep people busy for awhile,” said Messenger mission scientist David Lawrence of Johns Hopkins University Applied Physics Laboratory at the conference. The new iron-rich picture of Mercury’s surface that’s emerging resembles that of Earth’s moon, Lawrence said. An error during the flyby caused Messenger’s power to turn off, and as a result, the team acquired only about 50% of the data they’d hoped for. But in addition to the neutron spectrometer measurements, Messenger imaged most of the planet, including 6% of the surface that has never been explored before. In one striking image, a double-ring basin 290 km in diameter resembles a feature discovered during the first flyby, known as the Raditladi basin. Both features, which are believed to be volcanic in origin, are only about a billion years old, a fact that bolsters evidence for recent volcanism on the planet, said Brett W. Denevi, a Messenger mission member and postdoc at Arizona State University, Tempe, at the conference.— ELIZABETH WILSON
NOVEMBER 9, 2009
NASA/JOHNS HOPKINS U APL/CARNEGIE I NSTI TUTION OF WASH INGTON
LIGHT COMMANDS ION CHANNEL
