increase stability, the researchers discovered, performing the experiment in an alpha helix, which is a common structural element of many proteins, including lysozyme. (Screws, slinkies, and stairways that wind around to save space are all examples of helices, as is DNA.)

One end of an alpha helix is positively charged, while the other end is negatively charged. By placing an opposite charge one turn of the helix from one of the end charges, the researchers found that they could raise the melting temperature of lysozyme by about 2°C. Several similar substitutions added further stability.

THE LEUCINE ZIPPER AND GENE REGULATION

From Oregon, Alber went to the University of Utah, where he was soon caught up in studies of the leucine zipper, collaborating with Peter Kim of the Whitehead Institute and several other researchers.

Leucine zippers are alpha helices that direct gene regulation. Gene regulation is the process that determines when the body will produce each protein. For example, eat a donut and the gastrointestinal tract must crank out the enzymes that digest starch. Then, as sugar enters the bloodstream, the pancreas must begin to manufacture insulin. Leucine zippers manage the regulatory process.

The work on leucine zippers ultimately would support Matthews's findings that, although most amino acids exert little influence on shape, that of core amino acids can be profound. Alber got caught up in the leucine zipper work as Kim et al. were piecing together the structure.

But it was Steven McKnight, of the Carnegie Institution of Washington

FIGURE 10.1 Side chains (thick lines) make contacts between the helices in a schematic drawing of a leucine zipper.



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