"We discovered a signature for activation that is in fact found in the cell and doesn't require these other synthetic groups," said Hubbard, first author of the study. "This was a critical result, which allowed us to bridge the gap between our biochemical and physiological findings.
"Next, we needed to identify precisely how resveratrol presses on SIRT1's accelerator," said Sinclair. The team tested approximately 2,000 mutants of the SIRT1 gene, eventually identifying one mutant that completely blocked resveratrol's effect. The particular mutation resulted in the substitution of a single amino acid residue, out of the 747 that make up SIRT1. The researchers also tested hundreds of other molecules from the Sirtris library, many of which are far more powerful than resveratrol, against this mutant SIRT1. All failed to activate it.
The authors propose a model for how resveratrol works: When the molecule binds, a hinge flips, and SIRT1 becomes hyperactive.
Although these experiments occurred in a test tube, once the researchers identified the precise location of the accelerator pedal on SIRT1and how to break itthey could test their ideas in a cell. They replaced the normal SIRT1 gene in muscle and skin cells with the accelerator-dead mutant. Now they could test precisely whether resveratrol and the drugs in development work by tweaking SIRT1 (in which case they would not work) or one of the thousands of other proteins in a cell (in which they would work). While resveratrol and the drugs tested revved up mitochondria in normal cells (an effect caused activating by SIRT1), the mutant cells were completely immune.
|Contact: David Cameron|
Harvard Medical School