Investigators at Argonne National Laboratory have devised a “bacterial factory” that enables the study of membrane proteins, that cannot be studied in an aqueous environment:
“The first step in studying most proteins is to dissolve them in water,” Hanson said, “but that does not work with membrane proteins that live in the oily, lipid bi-layer that surrounds the cell.” [Deborah Hanson is a biochemist at Argonne -ed.]
Researchers studying water-soluble proteins often use commercial E. coli -based systems to express, or produce, copies of the protein. When membrane proteins are produced in E. coli, they overload the cell’s bi-layers and cause the cells to die. The sources that have yielded the majority of the few known membrane-protein structures are organisms in which the target membrane protein is naturally abundant.
Laible and Hanson took advantage of the natural characteristics of the Rhodobacter species of photosynthetic bacteria they were working with in another project. Under certain conditions – in response to light or oxygen – Rhodobacter naturally produces large quantities of internal membranes.
The biologists developed a system that successfully expresses hundreds of copies of a chosen membrane protein in Rhodobacter while simultaneously synthesizing the internal membranes they want to live in.
So far the team has cloned about 500 genes into Rhodobacter. “First,” Laible said, “we produced a variety of membrane proteins of different sizes, functions and physical properties, and we have had a 60 percent success rate with them. Now we have cloned all of the membrane proteins of E. coli and are continuing production.”
As they continue to manufacture different membrane proteins, the team is tackling the next step to creating a pathway to protein crystallization for membrane proteins by developing specialized molecules, or reagents.
“We are working,” Laible said, “with a multidisciplinary team from the University of Wisconsin-Madison, the University of Illinois-Chicago and deCODE biostructures, Inc. of Bainbridge Island, Washington.” They will focus on three types of reagents:
1. Designer detergents that remove the membrane protein from the lipid bi-layer where it resides,
2. Antibodies to stabilize the membrane protein, and
3. Molecules that mimic the lipid bi-layer, or membrane.
Researchers will test the reagents on the membrane proteins produced in the Rhodobacter ‘factory.’
The press release…