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"What we did was to take this peptide that we knew could inhibit the binding and infection of measles and display it on the surface of the plant virus," says Manchester.

What Manchester and Johnson found was that not only were they able to protect cells from measles infection, but they were able to do so with at least 100-fold greater efficacy than with the peptide alone, and Manchester was able to prevent infection in vivo. The secret of the CPMV's success, they believe, is its polyvalency—the fact that it displays multiple copies of the anti-measles peptide.

"When the [cowpea mosaic] virus comes in contact with the measles virus, it's not just bringing one copy, but 60 copies," says Johnson. Moreover, the hemagglutinin molecule to which the peptides bind is a trimer and so binding is favorable. And they could potentially attach more than one peptide to the cow pea mosaic virus and target measles with even higher efficacy.

The same approach might be used to create a vaccine in the traditional sense by putting antigen molecules from measles or some other virus that would stimulate an immune response to block an infection from a later exposure.

One of the great advantages of using such an approach is its frugality—the virus does the work of making the peptide. This is an advantage for achieving Manchester's ultimate goal of making new vaccines, since one of the main criteria for any globally effective vaccine is its price.

Another preferential feature for a vaccine's success is its bioavailability, since delivering a vaccine to remote regions is made much more difficult if specialized equipment or training is required. And Manchester says that the modified CPMV looks reasonably orally bioavailable, based on some preliminary studies she completed with Finn.

Finn attached fluorescent dyes to the viral particles to see where they go in vivo and how long they last in tissues, and Manchester found that, indeed, the CPMV molecules are distributed throughout the organism. Now she and Finn are trying to make further improvements to this distribution by attaching polyethylene glycol molecules to the virions to dampen the immune response to them.

"If you coat a protein with polyethylene glycol, it tends to dramatically reduce its visibility to the immune system," says Johnson.

Bringing their Collaboration to the New Center

Finn, Johnson, Lin and Manchester are all part of the new Center for Integrative Molecular Biosciences (CIMBio) faculty and have laboratory space in the newly constructed CarrAmerica B building. CIMBio was designed to be the most advanced biological microscopy center in the world and to provide an environment in which the expertise and resources of many research groups could be combined.

Finn and Johnson provide a service to the center by providing tailored CPMV for the molecular microscopes and for the new automated processes. Since the structure is so well determined, it makes a good test bed to determine how well the electron microscopes are doing.

Finn will also conduct an independent program on basic research into new labels for electron microscopy. In EM, heavy atom labels are routinely attached to the particular molecules of interest in order to image these molecules. Currently, there are only a few commercially available labels.

"That's just not versatile enough for the kinds of applications this center is going to deal with," says Finn, adding that the result of his research into new labels will be a specialized chemistry service for researchers using the CIMBio facilities.

"We want biologists and biochemists to come to us with a problem, 'Here's a protein I need to label with a heavy atom residue' or 'I tried what's available and it doesn't work so well.' That's partly what we're here to do."

For the most part, though, Johnson, Lin, Finn, and Manchester are collaborating with each other to find and test uses for the modified CPMV particles. And they have many possibilities.

They have already successfully attached biotin (Vitamin B), sugars, and organic chemicals to the viral surface, and they can immobilize large molecules on the surface—whole proteins even.

"We can attach anything we want to the surface of the virus," says Johnson.

One possible attachment are molecules that can be used to image cancers or other biological states in living cells by labeling CPMV with an anti-tumor agent or some molecule that targets a particular biology of interest along with radiolabels or some other sensing agent that could be visible under magnetic resonance or microscope imaging.

Finn, Johnson, and Lin found that cysteines could also be double-labeled by placing cysteine on both the inside and outside of the virus shell and that a pattern of attachment sites could then be created that would allow for novel chemistry.

Catalysis could potentially be carried out with the virus particles. The temperature and pH stability, solubility, and the chromatographic properties of the virus can be altered at will, by adding the right molecules. And the virus particles can self-organize into network arrays in a crystal, which may make it a useful building block for various applications in nanotechnology, the field that seeks to build functional material on the nanometer scale (roughly one to one hundred billionths of a meter).

"You can, in principle, determine the type of assembly you get by programming the building blocks," says Finn.

And in collaboration with Manchester, Finn and Johnson are excited about the possibility of testing CPMV as a polyvalent delivery vehicle. Since there are 60 attachment sites, the virus will present multiple copies of the attached molecules wherever it goes.

"This is something uniquely Scripps," says Johnson. "We have three different departments, three different backgrounds, and yet here we are."


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The structure of cowpea mosaic virus complexed with 60, 1.4 nanometer, gold particles attached to specific cysteine residues on the particle surface. The structure was created by genetic engineering of the virus capsid subunits. The proteins of the virion are represented as ribbon drawings that show the location and fold of the 60 pairs of polypeptide chains that form the virus. The specific pattern of gold particles demonstrates that this virus can be used to generate attachment sites for creating new surface properties that may be useful in developing novel biomaterials.











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