The researchers also report how LeuT utilizes two binding sites on the outward-facing side to enable its function, consistent with their previous findings. Their latest evidence may help to settle a controversy about the number of binding sites in this transporter, Dr. Weinstein says. Thus, they found that the two binding sites must work cooperatively to transport molecules. When either site was mutated, alanine was incapable of causing the transporter to flicker between open and closed states. Therefore, substrate binding to both sites is necessary for altering transporter dynamics and recycling molecules.
"These results may lead to key insights into which binding sites mediate the specific effects of various drugs," says Dr. Javitch. Using computer simulations, the researchers described the molecular events that link substrate binding to changes in transporter conformation. In brief, binding at one site induces structural changes that propagate to the other site, causing the transporter to release its contents into the cell. "We're looking at an unprecedented molecular level at the mechanics of this protein and how the binding of the substrates causes conformational changes," Dr. Javitch says. "We think that our observations have broad relevance to how other sodium-dependent transport processes work."
The results will likely translate to mammals, including the transporters in human nerve cells, as bacterial and mammalian transporter
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New York- Presbyterian Hospital/Weill Cornell Medical Center/Weill Cornell Medical College