Garcia and his collaborator, postdoctoral researcher Henry Herce, initially set out to uncover how the peptide interacts with a lipid bilayer that is used to model the cell membrane. A highly efficient biological system, the cell membrane is composed of a lipid bilayer (made up of two monolayers) designed to protect the cell by preventing the influx of material. Each lipid in the bilayer has a polar, or charged, end and a non-polar end. A monolayer of lipids faces the exterior of the cell, with the polar end facing the outside of the cell. Another monolayer is under the first layer, forming the bilayer. The polar end of the lower layer faces the interior of the cell, forming a middle section containing the uncharged halves of both monolayers.
Because charged particles seek each other in order to neutralize themselves and achieve a more stable state, the surface of the polar cell membrane and the positively charged HIV peptide are drawn to one another. But the interior of the bilayer is not charged and forms a strong barrier against the entrance of any charged material.
As was expected, in their simulations the researchers observed that the positive charges in the peptide quickly attached to the surface of the cell membrane and sought out and reacted with negatively charged phosphates from the charged portion of the lipid bilayer to satisfy their need for neutrality. "Then the peptide entered the forbidden territory of the cell," Garcia said. The positively charged peptide entered the membrane. "This is when this mechanism starts to challenge conventional wisdom," he said.
The researchers' model systems show the peptides grabbing for
|Contact: Gabrielle DeMarco|
Rensselaer Polytechnic Institute