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Three-dimensional Structure of Physalis Mottle Virus: Implications for the Viral Assembly

Sri Krishna, S and Hiremath, CN and Munshi, SK and Prahadeeswaran, D and Sastri, M and Savithri, HS and Murthy, MRN (1999) Three-dimensional Structure of Physalis Mottle Virus: Implications for the Viral Assembly. In: Journal of Molecular Biology, 289 (4). pp. 919-934.

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The structure of the T=3 single stranded RNA tymovirus, physalis mottle virus (PhMV), has been determined to 3.8\AA resolution. PhMV crystals belong to the rhombohedral space group R 3, with one icosahedral particle in the unit cell leading to 20-fold non-crystallographic redundancy. Polyalanine coordinates of the related turnip yellow mosaic virus (TYMV) with which PhMV coat protein shares 32 % amino acid sequence identity were used for obtaining the initial phases. Extensive phase refinement by real space molecular replacement density averaging resulted in an electron density map that revealed density for most of the side-chains and for the 17 residues ordered in PhMV, but not seen in TYMV, at the N terminus of the A subunits. The core secondary and tertiary structures of the subunits have a topology consistent with the capsid proteins of other T=3 plant viruses. The N-terminal arms of the A subunits, which constitute 12 pentamers at the icosahedral 5-fold axes, have a conformation very different from the conformations observed in B and C subunits that constitute hexameric capsomers with near 6-fold symmetry at the icosahedral 3-fold axes. An analysis of the interfacial contacts between protein subunits indicates that the hexamers are held more strongly than pentamers and hexamer-hexamer contacts are more extensive than pentamer-hexamer contacts. These observations suggest a plausible mechanism for the formation of empty capsids, which might be initiated by a change in the conformation of the N-terminal arm of the A subunits. The structure also provides insights into immunological and mutagenesis results. Comparison of PhMV with the sobemovirus, sesbania mosaic virus reveals striking similarities in the overall tertiary fold of the coat protein although the capsid morphologies of these two viruses are very different.

Item Type: Journal Article
Publication: Journal of Molecular Biology
Publisher: Academic Press
Additional Information: Copyright of this article belongs to Academic Press.
Keywords: Assembly disassembly;Physalis mottle virus;Tymoviruses;Viral structure;X-ray diffraction
Department/Centre: Division of Biological Sciences > Molecular Biophysics Unit
Division of Biological Sciences > Biochemistry
Date Deposited: 09 Oct 2007
Last Modified: 19 Sep 2010 04:40
URI: http://eprints.iisc.ac.in/id/eprint/12134

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