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Metal Chaperones At Work
REBECCA RAWLS
Chemists at Northwestern University have captured the first snapshot of a metallochaperone protein at work. Audrey L. Lamb, a postdoctoral researcher in the laboratory of assistant professor Amy C. Rosenzweig, and colleagues have determined the X-ray structure of a chaperone protein that transports copper, complexed with its target enzyme, a superoxide dismutase called SOD1 [Nat. Struct. Biol., 8, 751 (2001)].
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HANDSHAKE Subunit of the enzyme SOD1, purple, joins with subunit from copper chaperone protein, whose various domains are shown in blue, green, and yellow. |
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"We have the first image of a structure that delivers copper to its target," Lamb says.
One-third of all known proteins contain metal cofactors that are almost always essential for the catalytic function of the enzyme. Yet little is known about how these often very reactive metals are transported within cells and inserted properly into the appropriate proteins.
In the case of the copper chaperone protein and SOD1, the Northwestern chemists find, both the chaperone and the target proteins ordinarily exist as dimers of identical subunits, and the interface between these two subunits is very similar in both proteins. The transfer complex contains one subunit from each protein.
The complex structure "shows how these two proteins recognize each other, and it goes a long way toward explaining how the actual transfer of the metal ion might take place," Rosenzweig explains. Joining similarly shaped subunits from a chaperone protein and a target may be a general route for transferring metals from one protein to another, she suggests.
"The findings are truly groundbreaking," says Valeria L. Culotta, professor of environmental health sciences at Johns Hopkins University. They provide "new insight--in remarkable detail--into a metal transfer mechanism."
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