The findings were detailed in a research paper appearing last week in Proceedings of the National Academy of Sciences.

Researchers know that when the virus infects a host cell, it interacts with the cell membrane in such a way that it is swallowed up by the membrane and enters the cell as an "endocytotic particle." The Purdue researchers have now developed a theory for the mechanism behind the interaction and will test it in further research, Rossmann said.

Once the virus penetrates the host cell, the viral membrane fuses with an internal membrane in the cell. This process causes the virus particle to empty its contents inside the cell and leads to infection.

To study how the antibodies and E proteins attach, Kaufmann first separated the antibody's tail end from its two grasping, fingerlike structures called "antigen binding fragments."

"We don't want to handle the whole molecule, so we cut off these antigen binding domains and then combined them with the virus, forming the virus-antibody complex," Kaufmann said.

The researchers then used an electron microscope and a process called cryoelectron microscopy to take detailed pictures of this complex. Then they computed a three-dimensional model based on these pictures showing the outstretched antigen binding fragments attached to the virus particle.

The E proteins in one triangular segment of the icosahedron are not all positioned the same way relative to each other and to the various "axes" that define the icosahedron. This difference in position appears to be crucial in the binding process.

The antibody is called a monoclonal antibody because it recognizes only a single binding site on the E protein. Each E protein has three "domains," or well-defined, folded segments. The third domain has a structure commonly seen in molecules that attach to proteins to perform a specifi
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Contact: Emil Venere
venere@purdue.edu
765-494-4709
Purdue University
14-Aug-2006