Researchers get first peek at amylo...( In this case it was a yeast prion a ...)

In this case, it was a yeast prion, a misfolded protein that has the additional knack of being able to infect other cells or organisms, said first author Rebecca Nelson, a graduate student. Unlike in people, the yeast prion causes a condition which may be beneficial. In people, scientists do not know the role of the fibrils in the disease process in most associated diseases, but the formation of fibrils is associated with diseases.

According to yeast prion expert Jonathan Weissman, an HHMI investigator at the University of California, San Francisco, determining this structure "is a monumental achievement that will open up a new era in the structural analysis of amyloids."

The path to the discovery began several years ago, when co-author Melinda Balbirnie had narrowed down the stretch of prion necessary for fibrils to only seven amino acids, which were located at one end of the entire protein. Filling a test tube with just those snippets was enough to form short thin threads with the same essential characteristics of the common amyloid spine, a structure known as a cross-beta sheet.

Once it begins, the structure of a growing amyloid fiber is irresistible to other identical proteins or, as in this study, the crucial peptide subcomponents. The fibril spine elongates as pairs of the short beta-sheet segments stack up like teeth in a zipper.

When Balbirnie added more peptides to the test tube, she found that microcrystals formed and dropped to the bottom of the test tube. The crystals were about 50,000 times smaller than those normally used to determine atomic details of protein architecture. The researchers tried one mathematically intensive technique to analyze the microcrystals. It showed a fuzzy picture similar to other fibrils, telling them they were on the right track but not giving them the details they were seeking.

Nelson picked up the project four years ago. "Because the crystals were so small, we ended up trying lo
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
8-Jun-2005

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