They're tiny, erect shells that make architects green with envy, and can still destroy their surroundings. A study in contrasts: plant virologist Dr. Katharina Hipp of the University of Stuttgart's Institute of Biomaterials and Biomolecular Systems (BIO) and its Department of Molecular Biology and Plant Virology studies the African cassava mosaic virus, a cassava plant parasite, while her colleague Dr. Sabine Eiben finds some good qualities in the tobacco mosaic virus. Viruses may lend wings to nanotechnology in future as a basis for sensors, a support framework for tissue substitutes, or even in cancer diagnostics.
Katharina Hipp has been fascinated by geminiviruses, since the day when she listened as a young student to a lecture at the Department of Molecular Biology and Plant Virology at the Institute for Biomaterials and Biomolecular Systems. Her eyes glow as she gently rotates and tilts a model of the cassava mosaic virus, a member of the geminiviruses, between her fingers. The model, a parting gift from a former doctoral student, was printed out on a 3D printer according to the high-definition structure the two had worked out from many blurred electron microscopic projection images of a virus particle.
"What sets geminiviruses off from all other viruses is their protein envelope, which forms two incomplete icosahedra – whence the Latin name 'gemini', for 'twin'" explains biologist Hipp, who is now a post-doctoral researcher in the department headed by Holger Jeske. "Normally, we would expect these twin pairs to break apart easily, but that doesn't happen here." This still surprises Hipp. Viruses normally appear as rods, nearly spherical polyhedra, or – as here – as individual icosahedra.
Even though the geminiviruses are only about 20 to 35 nanometers in diameter (one nanometer = one millionth of a millimeter) and are thus pygmies among the viruses, and get by with only a minimum set of proteins, they cause considerable damage to many crop plants, primarily in the earth's tropical and subtropical zones. The African cassava mosaic virus initially betrays its presence by a "mosaic" pattern of light and dark-green areas on the leaves of the infected cassava plant, after which the entire plant wastes away. To make her point, Hipp says, "The cassava root is part of the basic diet of many in Africa and Southeast Asia, where it's as important as the potato once was for us." Many small farmers cultivate cassava behind their houses to feed their families. If the harvest fails due to a virus, the situation is dramatic for the people there."