NEWS OF THE WEEK SCIENCE
STUDYING ZINC IN METALLOPROTEINS NMR technique allows direct observation of catalytic zinc centers
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BOUT A THIRD OF PROTEINS
are metalloproteins, and many of these contain the essential catalytic metal zinc (Zn2+). But there has been no way to study the metal centers of Zn2+ proteins by nuclear magnetic resonance spectroscopy (NMR)— or most other spectroscopic techniques, for that matter. There is now An NMR technique for observing Zn2+ has been devised by technical group leader Paul D. Ellis and colleagues Andrew S. Lipton, Garry W. Buchko, Jesse A. Sears, and Michael A. Kennedy of the W R. Wiley Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory (PNNL) tf.Âm. Chem. Soc, 123, 992(2001)}. Researchers have long been frustrated by the difficulty of studying Zn2+ in metalloproteins. "It doesn't have a UV-Vis spectrum," Ellis explains. "It has no unpaired electrons, so you can't use electron paramagnetic resonance spectroscopy on it. And its NMR properties are poor," ruling out NMR analysis. "The net effect is that there was almost no way of telling what was happening at this very important catalytic metal in biological systems," he says—except for use of X-ray crystallography on proteins capable ofbeing crystallized and X-ray absorption fine structure spectroscopy Researchers have generally sidestepped this limitation with a surrogate probe strategy in which the Zn2+ ion in a metalloprotein is replaced with cobalt or cadmium, each of which is more easily studied spectroscopically HTTP://PUBS.ACS.ORG/CEN
But these substitutes don't always faithfully represent the properties of Zn2+. With the PNNL technique, a metalloprotein is cooled to a temperature from 5 to 25 degrees or so above absolute zero, which increases its NMR sensitivity A spin-echo method is then used to obtain quadrupole coupling constants and chemical shift data that reflect structure and bonding at the Zn2+ site. Using an NMRprobe that they designed, the researchers demonstrated the method on a 14.7-kilodalton (kDa) protein. But the sensitivity is sufficient to study proteins up to about 60 kDa. "The ability to perform successful zinc NMR studies on pro-
teins represents a major advance," says chemistry professor Gerard Parkin of Columbia University Surrogate probe experiments are still valuable, allowing one to learn more about mechanisms of action, he notes. "But being able to study the native enzyme is clearly a better way to go." Chemistry professorJames E. Penner-Hahn of the University of Michigan, Ann Arbor, calls the work "an extremely important development. Zinc proteins have not been as well studied as, for example, copper- and iron-containing proteins"—a problem the new technique could help solve, he says.—STU BORMAN
COOL P R O B E Sears (left), Ellis (center), and Lipton—shown holding their Zn 2+ NMR probe at the foot of Rattlesnake Mountain, a peak that overlooks their l a b are moving metalloprotein spectroscopy to greater heights.
GOVERNMENT
House Science Chair Boehlert Makes His Intentions Known romising to "fight to increase research funding in general and funding for the physical sciences in particular," Rep. Sherwood L. Boehlert (R-N.Y.) last week delivered his first major policy speech since becoming chairman of the House Science Committee. "I want the committee, early on, to take a serious look at the balance within the federal research portfolio," Boehlert said, adding that "a cursory look at the numbers certainly gives one the feeling that things may be a little out of whack." During a speech at the Universities Research Association Inc. annual meeting in Washington, D.C., he outlined three immediate priorities for his committee: science and math education, energy policy, and the environment. They will be the subjects of the committee's first three hearings, he said, which are scheduled to begin in early March. Education is "perhaps the most pressing dilemma of the three," Boehlert said. "I don't have a ready set of solutions. What I do have is a set of questions that I hope will frame the committee's agenda as we put together an education program in concert with the Administration and other House committees." Boehlert said his questions include how to attract more top students into science and math teaching and how to ensure that technology actually improves education. Boehlert made it very clear that he is a friend of science. "I want to build the Science Committee into a significant force within the Congress," he said, "and I want to ensure that we have a healthy, sustainable, and productive R&D establishment."-WILLIAM SCHULZ
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