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Prions Under the Magnet

One of the largest areas of study in Wüthrich's laboratory involves prion proteins. Mis-folded prion proteins have been suggested to cause bovine spongiform encephalopathy, or mad cow disease, and a form of the same disease in humans, called variant Creutzfeldt-Jakob Disease.

Prion proteins are expressed widely throughout the body and sit anchored onto the surfaces of cells in a wide variety of tissue, particularly on cells in neuronal tissue.

Infectious, malformed prion proteins start out with one shape, which is innocuous, and end up with another shape, which is observed in organisms suffering from a deadly "prion" infection. Infectious prions from an animal with mad cow disease, for instance, are believed to transmit the disease by initially causing normal prion proteins in the brain of a healthy cow to misform into the infectious form. Then these prions will act on more normal prion proteins to produce more and more misfolded proteins that accumulate and eventually lead to a sponge-like build-up and brain damage.

Wüthrich concentrates on comparative studies of the normal form of the prion protein in various species.

"[We want] to get the molecular basis of the species barrier," says Wüthrich. "Why are there no records of transmission from sheep to man, but there is mounting evidence that there is transmission from cattle to man?"

The assumption is that the more similar the prions are across species, the easier the transmission will be, as in cows to humans.

"Our results so far show that the healthy forms of the prion protein between man and cattle are identical in the folded part of the molecule," says Wüthrich. Other species, he adds, show differences even though the global fold is maintained.

Wüthrich does not stop at cows. He has solved the structure of the prion protein from chickens, for instance, and he is almost done with that of the turtle.

Prions are interesting also because much of the molecule is unstructured. The protein has a long tail that is highly flexible and is as much at ten times longer than the diameter of the folded part of the protein. "By studying evolutionarily widely divergent species, we hope to possibly target some clues as to the natural function of the prion protein, anticipating that the active site would be preserved," says Wüthrich.

Wüthrich is also interested in making preparations of prion protein aggregates that could be used to study the misfolded protein and the molecular basis of the aggregation. The needs are tantalizingly simple: a sample of isotope-labeled prion protein in solution that form repetitious aggregates. But the difficulty is preparing a sample that aggregates only a little, from two to forty proteins in a clump, as opposed to one that forms fibrils and crashes out of solution.

"If we had such preparations of aggregated prion proteins, we probably would have data from TROSY and CRINEPT experiments already," says Wüthrich.

Works In Structural Genomics

Since the start of his laboratory at TSRI in October 2001, Wüthrich has also been collaborating with the Joint Center for Structural Genomics (JCSG), a $30-million effort to develop high-throughput technology that could one day support efforts to find and catalog the structures of all proteins active in the human body. The JCSG is a multi-institution collaboration sponsored by the National Institutes of Health and led by TSRI Molecular Biology Professor Ian Wilson.

With the JCGS, Wüthrich is planning to use NMR as a tool to test sample preparations. What is the effect on the fold of a protein, for instance, when you add a histidine tag, typically several consecutive histidine residues that allow the protein to be highly efficiently separated on a column.

The idea is to use NMR as a screening tool to evaluate the quality of protein preparations from the automatic procedures—to check on the results and tighten the biochemistry used to prepare the samples. Choosing a biochemical technique exclusively for its amicability to the automation process may not be the best solution, since in the end the most important thing is having pure, relatively unmolested samples.

"We have the potential with our technique to make a major impact," says Wüthrich.


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NMR structure of the bovine prion protein, bPrP(23-230). A well-defined globular domain comprising residues 123-230 is green. An impression of the state of a flexible "tail" of residues 23-122 is provided by a superposition of 40 grey lines representing snapshots taken at short time intervals.