Structures of plant viruses from vibrational circular dichroism

Abstract

Vibrational circular dichroism (VCD) spectra in the amide I and II regions have been measured for viruses for the first time. VCD spectra were recorded for films prepared from aqueous buffer solutions and also for solutions using D 2 O buffers at pH 8. Investigations of four filamentous plant viruses, Tobacco mosaic virus (TMV), Papaya mosaic virus, Narcissus mosaic virus (NMV) and Potato virus X (PVX), as well as a deletion mutant of PVX, are described in this paper. The film VCD spectra of the viruses clearly revealed helical structures in the virus coat proteins; the nucleic acid bases present in the single-stranded RNA could also be characterized. In contrast, the solution VCD spectra showed the characteristic VCD bands for a-helical structures in the coat proteins but not for RNA. Both sets of results clearly indicated that the coat protein conformations are dominated by helical structures, in agreement with earlier reports. VCD results also indicated that the coat protein structures in PVX and NMV are similar to each other and somewhat different from that of TMV. The present study demonstrates the feasibility of measuring VCD spectra for viruses and extracting structural information from these spectra. INTRODUCTIONA variety of different spectroscopic and diffraction techniques have been used for structural analyses of viruses. These techniques include electronic circular dichroism (ECD) in the UV-visible region, vibrational Raman optical activity (ROA), crystallography for spherical viruses and fibre diffraction for filamentous viruses. While crystallography and fibre diffraction have the potential to provide complete descriptions of virus structures, they depend on the availability of virions at high purity and in relatively large quantities, and the formation of well-ordered crystals or fibres. They are therefore often not practical sources of structural information. The spectra structure correlation in ECD spectroscopy depends on observing characteristic ECD bands associated with a particular structure (Homer & Goodman, 1975;Erickson et al., 1981). For proteins, such correlation can sometimes be misleading because of the overlap of ECD bands originating from the peptide backbone with those from aromatic groups. Specifically for viruses, differential light scattering, which is proportional to the fourth power of incident wavelength, can interfere with ECD bands. Furthermore, ECD spectroscopy is known to yield artefact signals when film samples are studied. ROA spectroscopy (Barron, 2004; Blanch et al., 2002) is ideal for aqueous solution samples, but fluorescence interference and the requirement for higher concentrations pose limitations in some cases. Also it has not yet been possible to undertake ROA spectroscopy for film samples. The abovementioned limitations can be avoided with vibrational circular dichroism (VCD) spectroscopy.VCD is a measure of the difference in absorption for left and right circularly polarized light in the infrared (IR) region (Keiderling, 1981;Nafie, 1984;Polavarapu, 1998;Barr...

Peptide display on Potato virus X: molecular features of the coat protein-fused peptide affecting cell-to-cell and phloem movement of chimeric virus particles

“…pPVXCC and its derivative pPVXSma vectors, harbouring the mutated cp gene, were able to induce plant infections indistinguishable from those induced by the wild-type pPVX201 vector, with the formation of virus particles carrying genetically stable genomes. These data, together with a recent study aimed at defining PVX structure (Shanmugam et al, 2005), indicate that the formation of functional virus particles is not affected significantly by the removal of CP N-terminal amino acids. However, our observations also demonstrated that the fusion of heterologous peptides of varying length and composition to the truncated N terminus does not always result in systemic infection.…”

Architecture and Assembly of Virus Particles

“…Vibrational circular dichroism studies show that the NMV CP has a similar structure to that of PVX (Shanmugam et al, 2005). Vibrational circular dichroism studies show that the NMV CP has a similar structure to that of PVX (Shanmugam et al, 2005).…”

“…Vibrational circular dichroism of TMV, PapMV, NMV, and PVX has shown helical structures in the CP but not in the RNA (Shanmugam et al, 2005).…”

Vibrational optical activity

“…This is one of the reasons ROA has proved more useful than VCD for studies of biomolecules, especially proteins and carbohydrates, which has provided the impetus for the recent successful efforts to improve the efficiency and accuracy of ab initio ROA calculations. However, VCD spectra of proteins [130], and viruses [131], have been measured from small quantities of samples dried from H 2 O solution onto thin films.…”