Scientific Report 2005

Molecular Biology

An Icosahedral Scaffold for Biophysical Studies and Nanomanufacturing

T. Lin, J.E. Johnson, A. Chatterji, W.F. Ochoa, A. Stone, T. Ueno

Cowpea mosaic virus (CPMV) is an icosahedral plant virus with a diameter of 30 nm. Because of its exceptional stability, high yield, ease of production, structural information to the level of atomic definition, and accessible genetic programmability, the virus has been used as a model system for biophysical studies and has been engineered for applications in biotechnology and nanotechnology.

Assembly of Nanomaterials on an Icosahedral Scaffold

A quintessential tenet of nanotechnology is the self-assembly of components at nanometer scale to form devices. Although small molecules with novel electronic properties can be synthesized, it is generally difficult to get functional connectivity among the different components in designed patterns. In contrast, because of their versatility, programmability through genetic engineering, and propensity to form arrays, biological macromolecules are more amenable for self-assembly either as devices for direct use or as scaffolds for patterning small molecules. We showed that CPMV can be used as a template for nanochemistry by introducing unique cysteine residues and exploiting the native lysine residues. In collaboration with B.R. Ratna, Naval Research Laboratory, Washington, D.C., we used the viral capsid as a nano circuit board and the reactive groups as anchoring points for the assembly of electronic molecules, oligophenylene-vinylene and others. The establishment of the molecular network was demonstrated by measuring electronic conductance via scanning tunnel microscopy.

High-Pressure Crystallography

Using high pressure, we markedly improved the diffraction from the cubic crystals of CPMV from about 4-Å to 2.1-Å resolution. If this use of pressure is generally applicable, it can have a marked effect on structural biology. To this end, we carried out mechanistic studies of the pressure-induced rectification of crystal imperfection.

Two types of cubic crystals were assigned to either an I23 or a P23 space group. The 2 types had the same rhombic dodecahedral morphology at atmospheric pressure. The crystals assigned to the I23 space group diffracted x-rays to higher resolution than did those assigned to the P23 space group. The assignment of the P23 space group was due to the presence of reflections with indices h + k + l = (2n + 1) (odd reflections), which are forbidden in the I23 space group. Analysis of the odd reflections from the P23 crystals at atmospheric pressure indicated that they originated from a rotational disorder in the the I23 crystals. The odd reflections were eliminated by applying 3.5 kbar of pressure, which transformed the crystals from the apparently primitive cell to the body-centered I23 cell, with dramatic improvement in diffraction.

Publications

Blum, S.A., Soto, C.M., Wilson, C.D., Brower, T.L., Pollack, S.K., Schull, T.L., Chatterji, A., Lin, T., Johnson, J.E., Amsinck, C., Franson, P., Shashidhar, R., Ratna, B.R. An engineered virus as a scaffold for three-dimensional self-assembly on the nanoscale. Small 1:702, 2005.

Chatterji, A., Ochoa, W., Shamieh, L., Salakian, S.P., Wong, S.M., Clinton, G., Ghosh, P., Lin, T., Johnson, J.E. Chemical conjugation of heterologous proteins on the surface of cowpea mosaic virus. Bioconjug. Chem. 15:807, 2004.

Chatterji, A., Ochoa, W.F., Paine, M., Ratna, B.R., Johnson, J.E., Lin, T. New addresses on an addressable virus nanoblock: uniquely reactive Lys residues on cowpea mosaic virus. Chem. Biol. 11:855, 2004.

Chatterji, A., Ochoa, W.F., Ueno, T., Lin, T., Johnson, J.E. A virus-based nanoblock with tunable electrostatic properties. Nano Lett. 5:597, 2005.

Falkner, J.C., Turner, M.E., Bosworth, J.K., Trentler, T.J., Johnson, J.E., Lin, T., Colvin, V.L. Virus crystals as nanocomposite scaffolds. J. Am. Chem. Soc. 127:5274, 2005.

Girard, E., Kahn, R., Mezouar, M., Dhaussy, A.-C., Lin, T., Johnson J.E., Fourme, R. The first crystal structure of a complex macromolecular assembly under high pressure: CpMV at 330 MPa. Biophys. J. 88:3562, 2005.

Lin, T., Schildkamp, W., Brister, K., Doerschuk, P.C., Somayazulu, M., Mao H., Johnson, J.E. The mechanism of high-pressure-induced ordering in a macromolecular crystal. Acta Crystallogr. D Biol. Crystallogr. 61:737, 2005.