Mar. 3, 2000 FAYETTEVILLE, Ark. -- In the world of proteins, change is usually bad: a simple change in an amino acid, a protein building block, can make the whole structure fall apart. But University of Arkansas researchers have made amino acid changes that instead have created a more stable protein. Medical and industrial processes that use proteins could benefit from this kind of increased protein stability.
Wes Stites, associate professor of chemistry and biochemistry, recently presented the team's findings at the Biophysical Society meeting in New Orleans.
The importance of protein stability lies as close as the soft drinks in your refrigerator. The high-fructose corn syrup that sweetens soda is treated with enzyme beds that eventually wear out, Stites said. More stable enzymes would last longer and reduce costs in this and many other industrial applications.
Stites and his colleagues study Staphylococcus nuclease, a model system for protein structure change. They make mutant proteins by changing a single amino acid, then subject them to heat or chemicals to see how well they hold together.
Most of the time, the mutants turn out to be wimpy, breaking down before their normal counterparts would. Out of 400 to 500 mutants created in Stites' lab, only seven have increased the protein's stability.
But when Stites and his colleagues combined the stabilizing amino acids into one protein, they created the largest increase in stability ever achieved in a protein. The altered protein remained stable at temperatures of more than 20 degrees Celsius higher than the original protein could withstand.
"This shows that it may be simpler than people thought to increase protein stability," Stites said.
In recent years many researchers have looked to thermophiles, organisms that thrive in hot springs and geysers, to study proteins that are stable at high temperatures. They have compared these proteins to ones with regular temperature stability.
" They found a lot of differences between the two types of organisms. But it's not clear what's important for stability," Stites said. One theory attributes thermophiles' high-temperature affinity to how the protein is packed. Proteins consist of long strands of amino acids, and these strands fold together to form a secondary structure in a process called packing.
Thermophiles have fewer internal spaces in their final structures than their low-temperature counterparts because the amino acids are stacked together more efficiently.
Stites found that the changes made in S. nuclease also improved packing, implying that good packing is a secondary effect, instead of a cause as researchers previously thought.
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