�Cells are expected to respond defensively when an antigen lands on a cell membrane and prepares to cause mischief.
But to activate a response, a cell must become aware of the presence of the intruder on its membrane, just as a human first must turn aware of a mosquito on a forearm in order to slap it.
In joint experimental work, physicists at Sandia National Laboratories and biologists at the University of New Mexico's Cancer Research and Treatment Center sustain combined unusual techniques to make real time movies that show precisely how a 50-nanometer-thick tissue layer notifies the cell it encloses that a hostile alien presence an antigen has made a landing.
And also wherefore notification may not assume place.
"We were able to characterize the motion of the receptor proteins in the tissue layer in real time as they respond to the antigen," says lead Sandia researcher Alan Burns. "Perhaps more importantly, we knowing the cell membrane is really complicated and highly structured, rather than liquid and unstructured, as is the dominant notion."
The membrane structures, which resemble holding corrals, says Burns, do move around in the membrane. But they restrict the motion of proteins. The response of the cell requires that the antigen receptor proteins bunch with other proteins to commence the cellular signaling network.
"The proteins are care Paul Revere giving a warning," says Burns. "When proteins bind antigens, they begin to cluster. This causes early proteins to thrash around. That sends a message from the membrane to the cell nucleus that something's wrong.
"But if at that place are places on the membrane that are walled off and an antigen lands there, the cell may not be notified there's a problem. No protein, no warning."
UNM researchers already knew that incoming antigens were detected by proteins present in the lipid ground substance of the cell membrane. But how exactly to determine the process?
Burns, on the job with his former Sandia postdoctoral educatee Keith Lidke (now a UNM prof), modified a special microscope called a total internal reflection fluorescence (TIRF) microscope, whose laser-light output is completely contained within the microscope coverslip. This resembles the way optical fibers transport lightheaded, except that the TIRF does non ever release any light-headed. But though the light is contained, making its use seem at low an exercise in futility because it penetrates nothing external, it generates a tiny electrical exploratory field that extends about one C nm into the cell, which lies supported by the coverslip.
"When a cellular telephone settles on a musical composition of bare thin glass," says Burns, "the membrane of the cell by definition is snuggled up against the glass and available to the radiation field."
Enter the UNM biology team. Led by prof Diane Lidke, the team was able to attach quantum dots of 8 nm and 11 nm respectively to two different types of antigen receptor proteins in the membrane.
Quantum dots emit light when stimulated by an electrical field. The color fluoresced is determined by the size of the back breaker. So one protein, when stimulated by the laser's electrical field, emitted orange River light. The other emitted red. That way researchers could keep track of the motion of single, individual proteins and find out how they interacted; what is more, it allowed them to observe barriers to the motion.
Sensitive CCD cameras picked up and videotaped the motion of the lit-up proteins as they reacted to the introduction of antigens to the membrane.
"It was like using cameras to follow individual bank robbers impress around as a armed robbery progressed," says Burns.
The act upon is of interest to Sandia, a national defense lab interested in determinant the human response to bioinfectious diseases, and to UNM's bioscience program.
Other authors on the paper were graduate educatee Nicholas Andrews and pathology professors Bridget Wilson and Janet Oliver, all with UNM's Cancer Research and Treatment Center.
The Sandia sour was funded by its Laboratory Directed Research and Development function. The National Institutes of Health funded the UNM portion.
The solve was published online the week of July 20 in the journal Nature Cell Biology.
Sandia is a multiprogram testing ground operated by Sandia Corporation, a Lockheed Martin company, for the U.S. Department of Energy's National Nuclear Security Administration. With independent facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic fight.
Sandia National Laboratories
PO Box 5800-0165
Albuquerque, NM 87185
United States
http://www.sandia.gov
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