NEWS OF THE WEEK STRUCTURAL
BIOLOGY
PROTEIN'S LIPID COAT REVEALED High-resolution structure of membrane protein captures its lipid environment
R
ELATIVELY LITTLE IS KNOWN
about how membrane proteins interact with the lipids that surround them because structural studies typically fail to capture these proteins' lipid environment. Now, a high-resolution structure of a membrane-embedded water channel protein has opened a window to how lipids pack around membrane proteins (Nature 2005,438,633). "The key to an effective membrane is to get the packing of the lipids and proteins right," explains Anthony G. Lee of the University of Southampton, England, in an accompanying Nature commentary. T h e new structural data "clearly illustrate how this packing is achieved." T h o m a s W a l z of H a r v a r d Medical School and coworkers captured the 1.9-Â structure of aquaporin-0 (AQP0) immersed in an artificial lipid bilayer. AQPO is a water channel that is the most abundant membrane protein in the lens of the eye. They used electron crystallography, a wellestablished technique that employs the beam of an electron microscope to produce diffraction patterns from frozen twodimensional crystalline arrays. It's particularly powerful for imaging membrane proteins, Walz says, because "it allows them to be imaged in their native environment, the lipid bilayer." Previously, crystal structures of a number of membrane proteins have revealed a small number of specifically bound lipids. But the AQPO structure, which Walz solved with the help of Tamir Gonen, Yifan Cheng, and Stephen G Harrison of Harvard and YoshiWWW.CEN-0NLINE.ORG
nori Fujiyoshi of Kyoto University inJapan, provides a very different picture. In the structure, a thin shell of lipid bilayer surrounds the hydrophobic midsection of the protein. The lipid is dimyristoylphosphatidylcholine, a non-endogenous lipid with a zwitterionic "head" and two 14-carbon fatty acid "tails." The lipid molecules stack tail-to-tail, with their fatty acyl chains packed tightly around the protein's bumpy midsection. The resulting shell provides a uniform surface against which the rest of the lipids in the membrane can pack. Their heads interact with charged side chains on the hydrophilic portions of the protein that would typically be at the membrane-water interface. Walz suggests that the lipidprotein interactions observed in the structure may be representative of the "nonspecific interactions that occur between any S C I E N T I F I C
LIPID LAYER The AQPO monomer (yellow ribbon) is surrounded by a thin shell of lipid bilayer (purple ball and stick). Water molecules in the protein's central pore are shown as blue balls. membrane protein and the natural lipids in cell membranes." The lipid used in this study, however, is not found in natural membranes, so it remains to be tested whether endogenous lipids make similar interactions with AQPO, he admits. Eventually, structural biologists hope "to determine at a molecular level the arrangement of proteins in cell membranes," notes James Allen of Arizona State University. He calls the new study "an exciting advance toward that goal." Mark S. P. Sansom of the University of Oxford adds that "from a chemical perspective, this detailed picture of lipid-protein interactions should help us sort out the design rules of how to lock a macromolecule into a membrane."—AMANDA YARNELL
PUBLISHING
Royal Society Is Cautious About Open Access ritain's Royal Society has published a po sition statement warning of the potential costs of mandating free access to journal articles. The independent scientific academy says a hasty shift to open-access publishing could re duce learned societies' ability to support scien tific activities, kill off some existing journals, and even "hinder rather than promote the exchange of knowledge between researchers."
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The society does not oppose open access. In fact, it provides free access to its journal articles 12 months after publication. But the society says some research funders, particularly in biomedicine, are lobbying for an "increase in the pace at which Web-based open-access journals, reposi tories, and archives are being developed, with the
emphasis on immediate open access." The soci ety "believes that there is a lack of consideration of the potential impact" of such changes. Part of the support for free access is coming from the Wellcome Trust, the U.K.'s largest non governmental funder of biomedical research. In October, the trust began requiring its grant recipi ents to deposit their research papers in the openaccess PubMed Central article repository for re lease within six months of publication. Research Councils UK, whose member coun cils are Britain's leading public funders of sci ence, is due to update its stance on open access in late December or early January. RCUK published a preliminary policy in support of open access in June.-SOPHIEROVNER
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