May 18, 1998 What would you think if your doctor wanted to inject you with a virus as a part of your medical treatment? Though still a long way off, that is just one of the implications of a recent breakthrough by Temple University chemistry professor Trevor Douglas and Montana State University plant pathology professor Mark Young. The results of their research appear in the May 14 issue of Nature.
Douglas and Young have utilized a "gating mechanism" in the protein coats of some simple viruses which allows them to admit and expel organic and inorganic material. Through these "reversible structural transitions" technicians will be able to remove the genetic component of a virus (the DNA or RNA that allows the virus to reproduce) and use the remaining protein coat as a container and delivery system for other substances.
Douglas and Young explain that "In their native state, viruses are protein assemblies which act as host containers for nucleic acid storage and transport. We have subverted this natural function." Their work is, to a large extent, a conceptual breakthrough. To see (and prove) that viruses are substances that can be taken apart, purged of genetic material, reassembled and used as couriers of selected substances is a significant challenge to conventional thinking.
Hope for significant medical advances come from the fact that the two researchers were able to load an organic substance similar to heparin--which is routinely used to treat coronary thrombosis--into cowpea chlorotic mottle virus. Because this phenomenon of gating is possible for a large number of viruses of different shapes and sizes, there is no reason to think that options for drug delivery are limited to any particular class of medicines.
The simple protein coats that Douglas and Young work with can also be "easily and routinely modified by design." This means that the loaded virus can be altered to target certain types of cells (like cancer cells) and holds the promise of being able to deliver drugs to very specific sites.
Young points out that the viruses he and Douglas work with are relatively simple plant viruses which 1) "are incredibly host-specific" and do not use animals as hosts; 2) are routinely and safely eaten by humans as part of vegetable material; and 3) have had their genetic material removed, leaving only a coat which can be used as a container. As such they pose no health threat to humans.
In fact, some of the most interesting implications of this study have nothing to do with traditional biology or biochemistry. Douglas and Young have used the protein coats of viruses as "size and shape constrained" chambers in which minerals crystallize in very specific and precise dimensions. The possibility of creating an unlimited number of homogeneously sized crystals would have a profound impact, for example, on the production of minaturized semiconductors and other patterned materials.
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