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September 25, 2008

STRUCTURAL BIOLOGY

Opsin's Active Conformation Revealed

Crystal structure of G-protein-coupled receptor provides new insight for how this class of proteins senses chemical and light signals

Sarah Everts

Patrick Scheerer/© 2008 Nature
TRANSDUCER The active form of the GPCR receptor senses everything from light to hormones in animals.

Light, odors, taste, and hormones are all sensed by G-protein-coupled receptors (GPCRs), a family of proteins responsible for detecting and transducing signals across cell membranes in life-forms as diverse as worms and humans. Because of their ubiquity, GPCRs are hotly pursued as drug targets by the pharmaceutical industry. Several X-ray crystal structures have been reported for different versions of the membrane-bound receptors, but all of them capture the protein in its inactive form.

Now, an international group of researchers from Germany, England, and South Korea is unveiling an active form of the receptor (Nature 2008, 455, 497).

The trick was accomplished by crystallizing the receptor with a peptide from the affiliated G-protein that docks into the active form of the receptor, explains coauthor Klaus Peter Hofmann, a biophysicist at the Medical University of Berlin Charité. The structure reveals a large tilt of one of the membrane-bound helices with respect to a seven-helix bundle also nestled in the membrane; the tilt creates a binding site for the G-protein ligand.

The elusive activated-state structure is a "long-awaited breakthrough," Thue W. Schwartz of the University of Copenhagen and Wayne L. Hubbell of the University of California, Los Angeles, note in an accompanying Nature commentary.

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Chemical & Engineering News
ISSN 0009-2347
Copyright © 2009 American Chemical Society

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