For a protein, shape is everything. Proteins contain many twists, turns and folds which help them fulfill their many roles, from shuttling energy within the body to providing "docking sites" for hormones, drugs and other chemicals. But when proteins break down and unravel -- when they lose their nooks and crannies -- they become useless.
Scientists from the University of Rochester, along with colleagues from the University of British Columbia, have genetically engineered a new version of the widely studied molecule cytochrome c, an indispensable protein found in all living organisms. The new protein holds together and remains folded under higher temperatures than the natural protein; in addition, yeast into which the new protein is injected grow faster than "normal" yeast. Its creators believe the new protein represents the largest increase in stability of any genetically engineered protein which functions properly over its natural counterpart.
The work is described in the June 25 issue of the Journal of Biological Chemistry.
George McLendon, Tracy Hyde Harris Professor of Chemistry at the University, and Fred Sherman, professor of biochemistry at the University's Medical Center, changed just one amino acid in cytochrome c, replacing an asparagine molecule with an isoleucine molecule. Since a protein's shape is determined by the sequence of amino acids, this one tiny change was enough to produce the new protein.
"In the natural protein, asparagine has no preference whether it is folded toward the inside or the outside," says McLendon. "But isoleucine prefers to be tucked inside, away from water. This preference makes our protein more stable."
Cytochrome c is found in the mitochondria, or "power packs," of cells. The protein acts much like a "biological battery," says McLendon. "Cytochrome c plays a role in keeping cells alive by converting energy. It reduces oxygen to water, and glucose to carbon dioxide."
McLendon says the importance of the discovery may not lie so much in the increase in stability of cytochrome c (from 45 to 62 degrees Celsius). Rather, it points toward an era when scientists may be able to predict and precisely design proteins with specific properties.
"We know that proteins' shapes control everything they do, but it's a big puzzle why they adopt the shapes they do," says McLendon. "We took something that has been selected by evolution, and we made it a lot more stable. If we can start to understand how this works, it would be useful for biotechnology applications, such as the industrial use of enzymes or the manufacturing of drugs."
A surprise to the scientists is that the engineered protein actually works better than the natural one.
"You seldom create something that actually grows better," says Sherman. "Because the change is so simple, we have to ask ourselves why this change hadn't occurred in nature on its own many years ago.
"Perhaps our protein has some disadvantages we haven't discovered yet," says Sherman, who adds that he and McLendon are studying cytochrome c further.
This work was supported by the U.S. Public Health Service, the National Science Foundation, and the Medical Research Council of Canada.
tr
CONTACT: Tom Rickey, (716) 275-7954