PHYSIOLOGY
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Olfactory bulb To cortex
Laureates' research has demystified the sense of smell
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WO U.S. RESEARCHERS HAVE
won this year's Nobel Prize in Physiology or Medicine for shedding light on the inner workings of the sense of smell. Scientists had long wondered how the olfactory system recognizes and remembers more than 10,000 different odors. Richard Axel, 58, a Howard Hughes Medical Institute investigator and professor of biochemistry and mo-
lecular biophysics at Columbia University and Linda B. Buck, 57, an H H M I investigator at Fred Hutchinson Cancer Research Center, Seattle, share this year's Nobel Prize in Physiology or Medicine —and its nearly $1.4 million cash award—for solving this mystery Most scents arise from a cocktail of molecules known as odorants—peppermint, for instance, gets its characteristic odor from a mixture that includes menthol, menthyl acetate, and menthyl valerate. Olfactory researchers had been hunting for the proteins expected to bind and sense odorants in the nose but had come up empty-handed. That scenario changed in 1991 when Axel and Buck, then a postdoc in Axel's lab, published a paper describing a large family of genes that code for membraneHTTP://WWW.CEN-ONLINE.ORG
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spanning receptor proteins found in a small patch of cells inside the nose. Mice make an astonishing 1,000 or so different kinds of these odorant receptor proteins. Humans, who don't rely as much as mice on their sense of smell, make about 350 different ones. Axel and Buck showed that these odorant receptor proteins belong to a family of proteins called Gprotein-coupled receptors, a class
that also includes the rhodopsin proteins that initiate vision. "Olfactory research can be divided into two eras: before and after this paper," comments olPHYSICS
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HOW THE NOSE KNOWS Axel and Buck figured out how the binding of odorants (geometrical shapes at bottom) to protein receptors on the surface of cells in the nose causes electrical signals to be sent first to a region of the brain called the olfactory bulb and then on to the parts of the brain that control thought and emotion. factory researcher Peter Mombaerts of Rockefeller University "While the term 'breakthrough,' is all too often used, I believe this paper is one of the clearest examples," he adds. Later, Axel and Buck—who started her own lab after her postdoc stint with Axel—independently showed that each cell in this region expresses only one type of odorant receptor protein. Each odorant molecule in a given scent activates several different types of odorant receptor proteins. As a result, a given scent gives rise to a unique signature of activated cells, allowing the brain to recognize and remember more than 10,000 smells with only hundreds or so different kinds of odorant receptor proteins.—AM AN DA YARN ELL
PRIZE
Force That Holds Nucleus Together Is Recognized
T
he 2004 Nobel Prize in Physics has been awarded to three U.S. physics professors for their contributions to theories describing forces that govern the interactions of quarks. These subatomic particles are the fundamental building blocks of protons and neutrons. David J. Gross, 63, of the University of California, Santa Barbara; H. David Politzer, 55, of California Institute of Technology; and Frank A. Wilczek, 53, of Massachusetts Institute of Technology, discovered, through theoretical investigations, that the intensity of the so-called strong interaction—the force that holds atomic nuclei together—weakens as the distance between quarks decreases and strengthens
as the separation between quarks increases. The surprising phenomenon, first reported in 1973, is termed "asymptotic freedom." The unexpected nature of the force causes quarks to behave as free particles at infinitesimally small separations. The theoretical result led to the development of quantum chromodynamics, which is recognized by physicists as an important piece of the Standard Model. That model accounts for the electromagnetic forces between charged particles in addition to the weak and strong forces that are active in atomic nuclei. The prize money, nearly $1.4 million, will be divided equally among the three laureates.— MITCH JAC0BY C&EN
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1 1, 2004
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