A variety of synthetic methods have been used to fabricate nanoscale building blocks capable of forming ordered arrays. Now, scientists from Scripps Research Institute have looked to nature to expand this arsenal. Chemistry professor M. G. Finn, molecular biology professor John E. Johnson, and coworkers have engineered a plant virus to provide polyvalent virus particles with tailored reactivities that form highly ordered arrays [Angew. Chem. Int. Ed., 41, 459 (2002)].

	STAR-STUDDED Cryoelectron microscopy image shows gold clusters (yellow) covalently tethered to the virus' icosahedral protein shell (gray) at each of 60 cysteine residues inserted by site-directed mutagenesis. © 2002 ANGEWANDTE CHEMIE

Measuring 30 nm in diameter, cowpea mosaic virus (CPMV) consists of an RNA-encoded genome surrounded by an icosahedral protein shell made up of 60 identical copies of a viral coat protein. These virus particles can be isolated in gram quantities from leaves of infected plants.

Using the X-ray crystal structure of the virus as a guide, the Scripps researchers insert a single cysteine at a defined position on the coat protein. Viral particles assembled with this mutated protein display 60 reactive thiol groups in a regular, predictable pattern on their surfaces. The team has attached clusters of gold molecules as well as biotin, sugars, and organic molecules to these sites.

CPMV particles readily self-organize into different crystal forms under well-defined conditions. This "provides a convenient way to bring properties developed at the nanoscale on individual modified particles to the macroscale as millimeter-sized particle arrays," Johnson says.

"This work represents a milestone since it suggests that assembled virus particles can be treated as chemically reactive surfaces that are potentially available to a broad range of organic and inorganic modifications," notes plant sciences associate professor Mark A. Young of Montana State University. The technique, which could find application in materials science and molecular electronics, "should open the eyes of both chemists and virologists alike to the expanded potential uses of virus particles," he adds.

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