Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
For full article and contact information, see Angew. Chem. Int. Ed. 2002, 41 (3), 459 - 462
Sick Beans lead to Nanotech
Plant viruses as chemically "programmable"
building blocks for nanobiotechnology
Farmers get little joy from the cowpea mosaic virus, which attacks legumes. Chemists and molecular biologists at the Scripps Institute in La Jolla are, on the other hand, completely taken with this virus. They are not setting the tiny things loose on plants, however, but have something completely different in mind: the viruses are to act as chemically "programmable" nanobiotechnological building blocks.
The goal of nanobiotechnology is to construct everything from the tiniest of components for such things as microcomputers to entire microscopic robots. To achieve this, building blocks whose size is on the order of a few nanometers (1 nm = one millionth of a mm) are needed. The Scripps team had the clever idea of falling back on existing structures. With a diameter of about 30 nm, the virus particles, which can be obtained from infected leaves in large quantities, are ideal candidates.
The shell of the virus is an icosahedral structure consisting of 60 identical protein building blocks. In experiments with different fluorescence dyes, M.G. Finn, John E. Johnson, and their co-workers determined that each of the 60 protein units has a chemical "hook", which binds to exactly one dye molecule. These "hooks" protrude into the interior of the virus. Only small dye molecules can get inside to bind. Through directed mutagenesis, the Scripps team created a variation of the virus, whose protein units boast a second "hook", this time on the outer surface of the virus. This binding site is occupied considerably faster and at significantly lower dye concentrations than the inner one. Each of the binding sites can be "addressed" separately and can be occupied with different dyes, for example.
This doesn’t just work for dyes - in principle any molecule that has been equipped with the right "eye" to correspond to the "hook" can be coupled to the virus, allowing it to be chemically "programmed". "We thus get a very high local concentration of the coupled chemical reagents in or around the virus," explains Finn. Interesting new chemical and biological properties are expected: maybe some type of micro-reaction-chamber?
Mutants with many "hooks" can also be generated. Metal particles can be coupled on, and with such decorated viruses it could be possible to produce conducting nanoblocks. The natural virus is highly crystalline, so if modified viruses can also be made to crystallize, highly organized structures of the coupled molecules would result. Such structures refract light and could be used as opto-electronic components. Finn and Johnson envision that their marriage of chemistry, virology, and molecular biology will result in a host of useful applications, made possible by Nature’s ability to build tough little protein capsules.