ANOTHER FORCE TO STABILIZE PROTEINS STRUCTURAL BIOLOGY:
Unappreciated interaction is widespread, research shows
T
HE HYDROGEN BOND has company. Another
noncovalent interaction along the protein backbone might help proteins fold and maintain their three-dimensional structures, according to a new study in Nature Chemical Biology (DOI: 10.1038/nchem bio.406). Protein modelers may need to incorporate this interaction in their algorithms. Ronald T. Raines and coworkers at the University of Wisconsin, Madison, have studied the so-called n to pi-star (n→π*) interaction in a variety of systems for several years. They have now teamed up with Derek N. Woolfson and coworkers at the University of Bristol, in England, to show, using protein database searches, that this interaction occurs in nearly every protein. In the n→π* interaction, one of the lone pairs of electrons on a carbonyl oxygen in one amino acid overlaps with the π antibonding orbital of the carbonyl group in the adjacent amino acid. “Because it’s a main-chain interaction, it doesn’t matter what the side chains are,” Raines says. Any amino acid can form an n→π* interaction, but proline’s ring structure makes it especially suited because of the constraints imposed by the distance and angles necessary for orbital overlap. “What’s neat about this is that it’s short-range,” Raines says. “In the α-helix, the hydrogen bond is between the first and fifth residues.” In contrast, the
n→π* interaction is between adjacent residues. The n→π* interaction is typically weaker than a hydrogen bond, however. In addition, Raines, Woolfson, and coworkers find evidence for these interactions in nearly every type of secondary structure and even in seemingly unstructured regions of proteins. Raines thinks this interaction has been ignored for so long because of how people have tended to represent and think about protein structure. “If you look at the α-helix without considering quantum mechanics, you would never think of the n→π* interaction,” he says. “At a practical level, the work suggests that some geometric aspects are not properly accounted for in standard molecular SHORT-RANGE mechanics force fields,” says William F. The n→π* interaction DeGrado, a professor of biochemistry and occurs when a lone pair of biophysics at the University of Pennsylvaelectrons on the carbonyl nia. “We might have to wait to see how sigoxygen in one amino acid nificant this particular missing piece is in overlaps the π antibonding the overall picture” of protein modeling, he orbital of the carbonyl says. “But it is already clear that they have group in the adjacent identified an important feature that will amino acid. The light blue spark new interest and investigations.” and yellow represent the The work is notable for its willingness phases of the relevant to make bold claims about the ubiquity of orbitals. (Black = C, the n→π* interaction, according to Neville red = O, dark blue = N, Kallenbach, a chemistry professor at New white = H) York University. “This is risky, but changing the mainstream of current thinking has to be,” he says. “One still can’t be sure that n→π* interactions are the exclusive explanation for the geometrical correlations that they find. It is worth finding out.”—CELIA ARNAUD
ELECTRIC VEHICLES Batteries and battery materials get a big boost New models of electric cars are spurring demand for lithium-ion batteries and related raw materials. Last week, Ford Motor chose a subsidiary of South Korea’s LG Chem to supply lithium-ion battery packs for the all-electric Focus, which goes on sale in 2011. And German chemical firm Süd-Chemie said it would spend $77 million to build a plant in Candiac, Quebec, that will make lithium iron phosphate (LFP), a cathode material used in lithium-ion batteries. Earlier, General Motors chose the LG Chem subsidiary Compact Power to supply the batteries for GM’s all-electric vehicle, the Chevy Volt, also expected to debut next year. To boost consumer con-
fidence, GM said it would guarantee the Volt’s battery for eight years or 100,000 miles. The GM and Ford batteries will be produced at a new Compact Power plant that is under construction in Holland, Mich. The U.S. government is providing half of the cost of the $300 million plant through a grant announced last August as part of $2.4 billion awarded for battery and electric drive research under the American Recovery & Reinvestment Act of 2009 (C&EN, Aug. 10, 2009, page 9). President Barack Obama delivered remarks at the official groundbreaking ceremony in Michigan late last week. Süd-Chemie said the new LFP plant
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will employ a proprietary wet-chemistry process. The plant, to start up in 2012, will ultimately produce 2,500 metric tons of LFP annually, enough for about 50,000 all-electric cars per year or as many as 500,000 hybrid gas/electric vehicles. Süd-Chemie now operates LFP plants in St. Bruno, Quebec, and Moosburg, Germany, with combined capacity of 900 metric tons. Süd-Chemie and LG Chem are pursuing a young but potentially lucrative market. Steven Minnihan, an associate with market research firm Lux Research, expects global sales of lithium-ion vehicle batteries to reach $2 billion this year and grow to $6 billion by 2015.—MARC REISCH
NAT. C HE M. BIOL.
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