Using modern microscopy tools, scientists have been able to look at the molecules and molecular structures on viruses, cell walls and other biological surfaces, but they haven’t had any way of knowing what those molecules actually are. Molecular microscopy techniques have been "chemically blind"- until now.
In the September 1999 issue of Nature Biotechnology, a team of biophysicists introduce a new method in atomic force microscopy (AFM) that gives the instrument the capability of mapping not just the topographic features of biological molecules, but the specifics of their biochemistry as well. The technique can potentially be used for nanometer-scale mapping of biomolecules and for locating specific molecular receptor sites during biological processes, opening the door to a wide variety of biotechnology applications.
The authors – Anneliese Raab, Dirk Badt, Hansgeorg Schindler and Peter Hinterdorfer from the Institute for Biophysics at the University of Lintz, Austria; Wenhai Han from Molecular Imaging Corporation, Phoenix, Arizona; Sandra J. Smith-Gill from the Frederick Cancer Research and Development Center of the National Cancer Institute; and Stuart M. Lindsay of the Department of Physics and Astronomy at Arizona State University – describe the successful testing of a technique that adds data about the location of specific proteins to the detailed surface images created by an atomic force microscope. In the experiment, the team used AFM to determine the location to within a few nanometers of resolution of lysozyme molecules on a surface.
The technique attaches antibodies keyed to individual proteins to the tip of microscope’s sensitive probe. When an antibody reacts with the protein it is specifically targeted to, it creates a variance in the microscope’s reading when compared to a reading using a bare tip, thus showing the presence of the protein in the region being scanned. To help insure that the antibody-tipped probe is truly sensitive, a strand of polymer connects the antibody to the tip, providing a "tether" that allows the antibody wiggle and shift into position to better connect with the protein receptors. A magnetically excited cantilever makes the tip oscillate up and down to make the antibody disconnect and reconnect and keep the probe moving.
"What this means is that we can now determine the precise physical locations of specific proteins," said Lindsay. "All you have to have is the right antibody and you can find all the places its antigen is. The more antibodies you scan with, the more detailed the map will be.
"It’s exciting because we’ve been able to see these molecules for a while, and now we’ll be able to tell exactly what they are."
Lindsay points out that the technique is likely to have extensive applications in biotechnology. "If you know where the various proteins are in relation to each other, say on the surface of a virus, you can use that information to both locate specific receptor sites and to affect them through their adjacent molecules," Lindsay said.
The research was supported by grants from the Austrian Science Foundation, the Austrian Ministry of Science, the National Institutes of Health and the National Science Foundation.