Research in the Francis group is focused on the development of new synthetic methods for the construction of nanoscale materials. The central strategy involves the attachment of new functional components to specific locations on structural proteins, and the subsequent self-assembly of these conjugates into new types of materials with useful electronic and biological functions.
Controlled Growth of Nanocrystalline Arrays Using Cytoskeletal Proteins
Modern synthetic methods for the preparation of inorganic nanocrystals have yielded promising new components for optical and electronic device construction. However, the organization of these materials into functional assemblies remains extremely difficult, in part because the small size of nanocrystals (2-10 nm) is well below the spatial resolution of most lithographic techniques. An alternative approach could be provided by attaching these nanocrystals to specific sites on the surfaces of fiber-forming cytoskeletal proteins, such as actin. By controlling the polymerization of the actin conjugates with additional proteins and small molecule natural products, specified locations could be connected with wire-like arrays of functional materials. Once constructed, the arrays could be converted into conductive linkages, thus providing an entirely new method for nanoscale circuit construction.
Modified Viral Capsids for the Assembly of Core/Shell Materials
A second research area involves the synthesis of three-dimensional nanostructures from the self-assembling proteins that form the outer coats of viruses. For example, by selectively modifying the top and bottom faces of the satellite panicum mosaic virus capsid protein, new types of core/shell materials could be obtained after assembly. These structures could be developed into particles capable of targeting desired tissue types and releasing their cargo of drug molecules. Functionalized viral capsids could also provide new tools for the investigation of multivalent binding interactions that occur in biological systems.
New Methods for Site-Selective Protein Modification
A central theme in this research program is the modification of structural proteins in specific locations in order to achieve homogeneous and predictable assembly. Site-directed mutagenesis provides a powerful set of tools for this purpose, and will be used extensively. However, there are limitations associated with this technique, and therefore the development of new chemical approaches for protein modification will be pursued as well. This research will take advantage of the rapidly expanding set of organic reactions that can proceed in aqueous solution, and will utilize asymmetric ligands and catalysts to enhance the selectivity of protein modifications. Combinatorial reaction libraries will play an important role in this research area.