For Immediate Release:
June 1, 2000
Contact: Janet Haley
(617) 632-4090
Nancy Grodin
Office of Technology Transfer
(617) 632-5516
NEW TECHNIQUE ENABLES SCIENTISTS TO ISOLATE ELUSIVE CELL PROTEINS OFFERING NEW TARGETS FOR DRUG THERAPIES
BOSTON -- Researchers at Dana-Farber Cancer Institute have devised a new way to pluck specific proteins from the membranes of cells making it possible to obtain these key proteins in a pure, undamaged and highly-stable state--something that has been cumbersome and rarely successful in the past.
The new procedure--developed at the Institute and published in the June issue of Nature Biotechnology--comes at a critical time as scientists are putting the finishing touches on the first map of the human genome -- the complete catalogue of genes within human cells. However, the actual roles of the majority of genes, and the proteins made from them, remain unknown. With the new technique, scientists will be able to isolate concentrated "nuggets" of proteins and singularly study their functions.
"The type of proteins we're dealing with, known as transmembrane or integral membrane proteins, are involved in an enormous array of cell activities, but there hasn't been a good way to isolate and purify them so their individual roles could be studied," says Joseph Sodroski, MD, the study's senior author and director for the Center for AIDS Research at Dana-Farber. "The method we've developed will not only let researchers study these proteins in detail but also allow them to devise new therapies and drugs."
Most transmembrane proteins have been particularly difficult to isolate because, unlike proteins that sit either entirely inside or outside the cell membrane -- and can easily be made in truncated forms for study -- they coil through the membrane like threads holding a button on a shirt.
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.
The technique developed by Sodroski and his colleagues involves a transmembrane protein known as a "seven-spanner" because it loops through the cell membrane seven times, with small strands extending from either side of the membrane.
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.
"The beads become, in effect, artificial cells whose membranes are covered with a single type of protein in a pure, stable form," says the study's lead author Tajib Mirzabekov, Ph.D., "It gives us an unprecedented opportunity to study how these proteins function and respond to outside stimuli."
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.
A particular class of transmembrane proteins -- including the one utilized in the Dana-Farber study -- represents one of the most promising targets for new drugs and therapies. These "G protein-coupled receptors" (GPCRs) interact with a class of proteins known as G proteins. 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. In fact, it's estimated that 60 percent of all existing drugs target GPCRs. Thus far more than 1,000 types of these proteins have been identified.
"Clearly, GPCRs represent an enormous opportunity for new therapeutics," Sodroski says. "By being able to study pure samples of these proteins, we'll gain insights into their function that may result in new approaches to treating a variety of conditions."
Dana-Farber Cancer Institute (www.dana-farber.net) is a principle teaching affiliate of Harvard Medical School and is among the leading cancer research and care centers in the United States. It is the only cancer center in New England to be both a federally designated Comprehensive Cancer Center and a Center for AIDS research.
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