A Colorado State University researcher will join colleagues in Germany in using laser microscopy to track protein molecules on the surface of cells, research that may eventually lead to an understanding of how the immune system combats disease. George Barisas, professor of chemistry and microbiology, has developed techniques that can follow the movement of protein molecules on an immune system cell’s surface.
The joint research will seek to answer an important question: does a particular kind of protein, called an ";antigen presenting"; molecule, exist in certain places on a cell membrane or does it move there in response to some chemical signal? The answer could have important implications for how the body fights infection.
Barisas will conduct his collaborative research under the auspices of a 1999 Humboldt Award, a number of which are given annually by vote of German scholars and scientists.
Barisas’ prize will enable him to work with long-time collaborator Thomas M. Jovin, head of the Department of Molecular Biology at the Max Planck Institute of Biophysical Chemistry in G"ttingen.
According to Barisas, current thinking in biology has "lipid rafts"-a lipid is a fat-like substance-floating on the cell’s surface. The rafts are lighter than the surrounding membrane. Proteins that normally are distributed across the cell membrane clump together in response to certain stimuli, and, when they do, these clumps seem to move into the rafts. That, in turn, creates further signals within the cell.
"The notion is that these signaling molecules all concentrate in those lipid rafts, and that is in fact the current paradigm for (cellular) signaling," Barisas said.
By concentrating on what molecules are found in (or without) the lipid rafts and under what circumstances, he said, "this lipid raft hypothesis allows us to focus attention on a smaller region and a smaller set of molecules," narrowing the quest somewhat. Barisas and his German counterparts are interested in B-cells, an immune-system cell that produces antibodies, and particularly in the protein found on B-cell membranes called an "antigen-presenting" molecule that helps trigger the antibody-producing process.
According to Barisas, the number of antigen-presenting molecules on a typical B-cell surface is fairly low, about 20,000 per cell. The researchers are asking whether these molecules normally are excluded from lipid rafts but move there when the body’s immune system is challenged. The researchers will therefore be looking for high concentrations of antigen-presenting molecules in lipid rafts.
"The mechanisms for signaling in the immune system are incredibly complicated," Barisas said. "The lipid raft hypothesis gives us another tool to see what molecules are involved in those signaling systems."
"We want to know the sequence of molecular interactions that starts with a signaling mechanism and ends with the production of antibody to combat infection."
In addition to their basic quest, the researchers are breaking ground with innovative equipment uses. In his lab in Fort Collins, Barisas has been using a variety of laser-microscope systems to track individual cell-surface molecules that interest him. Key protein molecules on the cells’ membranes tend to stay within specified regions and rarely move outside those domains. Barisas wants to know why, starting with where the proteins can be found.
"The simplest way to do this is to put a tiny particle of gold on the protein and look at the tagged cells through a microscope attached to a high resolution videotape," he said.
"That’s stage one. Then we come back, digitize the images, put them on computer disks and view them in real time." In Germany, Barisas and his colleagues will use a new "confocal" microscope containing hundreds of tiny mirrors in a computer-controlled, programmable array that should provide even more detail about the movement of proteins on cell membranes.
"This is very basic science, but it keeps showing up in all kinds of areas and is clearly a broadly occurring phenomenon," Barisas said. "Our hope is that we can find ways to turn this knowledge to practical uses."