Anju Chatterji

Cowpea mosaic virus: from the presentation of antigenic peptides to the display of active biomaterials.

The potential of cowpea mosaic virus (CPMV), a plant icosahedral virus, for the presentation of foreign peptides and proteins is reported. The most prominent feature at the virus surface is a region of the smaller of the two coat proteins (S) which has been extensively used for the insertion of foreign peptides. Given the availability of the three-dimensional structure of the native virus and the amenability of foreign peptide-expressing CPMV chimeras to crystallisation, immunological data can be correlated with the conformational state of the foreign insert. The latter is influenced by proteolysis which occurs within the foreign inserts. In an effort to offer an alternative context for peptide expression, extensive exploration of a second region of the S protein is reported with respect to tolerance to small insertions. Moreover, to make CPMV suitable for a wider spectrum of presentation, a technique was developed to allow surface coupling of a peptide which can serve as the anchoring point for a range of proteins. This new approach is also widely applicable for the direct chemical cross-linking of peptides and full-length protein domains to the viral capsid.

Templated self-assembly of quantum dots from aqueous solution using protein scaffolds

Short, histidine-containing peptides can be conjugated to lysine-containing protein scaffolds to controllably attach quantum dots (QDs) to the scaffold, allowing for generic attachment of quantum dots to any protein without the use of specially engineered domains. This technique was used to bind quantum dots from aqueous solution to both chicken IgG and cowpea mosaic virus (CPMV), a 30?nm viral particle. These quantum dot?protein assemblies were studied in detail. The IgG?QD complexes were shown to retain binding specificity to their antigen after modification. The CPMV?QD complexes have a local concentration of quantum dots greater than 3000?nmol?ml?1, and show a 15% increase in fluorescence quantum yield over free quantum dots in solution.

Steric and Electrostatic Complementarity in the Assembly of Two-Dimensional Virus Arrays

A highly ordered assembly of biological molecules provides a powerful means to study the organizational principles of objects at the nanoscale. Two-dimensional cowpea mosaic virus arrays were assembled in an ordered manner on mica using osmotic depletion effects and a drop-and-dry method. The packing of the virus array was controlled systematically from rhombic packing to hexagonal packing by modulating the concentrations of poly(ethylene glycol) surfactant in the virus solutions. The orientation and packing symmetry of the virus arrays were found to be tuned by the concentrations of surfactants in the sample solutions. A phenomenological model for the present system is proposed to explain the assembly array morphology under the influence of the surfactant. Steric and electrostatic complementarity of neighboring virus capsids is found to be the key factors in controlling the symmetry of packing.

Long term storage of virus templated fluorescent materials for sensing applications

Wild type, mutant, and chemically modified Cowpea mosaic viruses (CPMV) were studied for long term preservation in the presence and absence of cryoprotectants. Viral complexes were reconstituted and tested via fluorescence spectroscopy and a UV/vis-based RNase assay for structural integrity. When viruses lyophilized in the absence of cryoprotectant were rehydrated and RNase treated, UV absorption increased, indicating that the capsids were damaged. The addition of trehalose during lyophilization protected capsid integrity for at least 7 weeks. Measurements of the fluorescence peak maximum of CPMV lyophilized with trehalose and reconstituted also indicate that the virus remained intact. Microarray binding assays indicated that CPMV particles chemically modified for use as a fluorescent tracer were intact and retained binding specificity after lyophilization in the presence of trehalose. Thus, we demonstrate that functionalized CPMV nanostructures can be stored for the long term, enabling their use in practical sensing applications.