Traditionally, scientists have sought to lift such proteins from the membrane with detergents. The problem is that if the proteins are not quickly returned to a membrane environment, they lose their natural folds and become useless for study. Investigators first use a detergent to remove the protein from the membrane, then mix in tiny magnetic beads whose surfaces are coated with a specific antibody. Antibodies, which help fight infection, normally move like guided missiles toward particular proteins. In this case, they attract those proteins to the beads, causing the tiny spheres to be covered with up to 100,000 protein molecules, all exactly alike.
Researchers then add a mixture of fats, or lipids, to the beads and remove the detergent.
The lipids take the place of the original cell membrane and hold the proteins in their natural shape and condition. Although the procedure described in the study involves only one type of transmembrane protein, it should be useful for other members of the seven transmembrane protein family as well, researchers say. The technique will give researchers a relatively easy way to see how such proteins interact with different kinds of cells and chemicals. These experiments will help scientists understand how the proteins behave in their normal state and how they can be influenced by other substances and chemicals. Depending on the type of receptor and cell they're in, G proteins send signals that play a role in everything from vision, taste, smell, nerve impulses, and immune responses.