Discoveries
New technique enables scientists to isolate elusive cell proteins
Dana-Farber researchers have devised a new way to pluck specific proteins from the membranes of cells and concentrate them in pure "nuggets" so their functions can be studied.
Tajib Mirzabekov, Ph.D.
"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 can be studied," says the study's lead author, Tajib Mirzabekov, Ph.D. "The method we've developed will not only let researchers study these proteins in detail, but also will allow them to devise new therapies and drugs."
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.
The technique developed by Mirzabekov 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.
Joseph Sodroski, M.D.
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 senior author, Joseph Sodroski, M.D. "It gives us an unprecedented opportunity to study how these proteins function and respond to outside stimuli."
"The type of proteins we're dealing with, known as transmembrane or integral membrane proteins, are involved in an enormous array of cell activities."
— Tajib Mirzabekov, Ph.D.
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.
This research was reported in the June 2000 edition of Nature Biotechnology.
