Polymorphism of turnip yellow mosaic virus empty shells and evidence for conformational changes occurring after release of the viral RNA

Abstract

Turnip yellow mosaic virus (TYMV) is a small isometric plant virus which decapsidates by releasing its RNA through a hole in the capsid, leaving behind an empty shell [R. E. F. Matthews and J. Witz, (1985) Virology 144, 318±327]. Similar empty shells (artificial top component, ATC) can be obtained by submitting the virions to various treatments in vitro. We have used differential scanning calorimetry, analytical sedimentation, and electron microscopy to investigate the thermodenaturation of natural empty shells (NTC, natural top component) present in purified virus suspensions, and of several types of ATCs. ATCs divided in two major classes. Those obtained by alkaline titration, by the action of urea or butanol behaved as NTC: their thermograms contained only one peak corresponding to the irreversible dissociation of the shells and the denaturation of the coat protein. The temperature of this unique transition varied significantly with pH, from 71 8C at pH 4.5 to 84 8C at pH 8.5. The thermograms of ATCs obtained by freezing and thawing, or by the action of high pressure, contained two peaks: shells dissociated first into smaller protein aggregates at 57 8C (at pH 5.0) to 61 8C (at pH 8.5), which denatured at the temperature of the unique transition of NTC. Shells obtained by heating virions to 55 8C at pH 7.6, changed conformation after the release of the viral RNA, as upon continuous heating to 95 8C, their thermograms were similar to those of the shells obtained by freezing and thawing, whereas after purification they behaved like NTC. Structural implications of these observations are discussed.

Thermal analysis of protein stability and ligand binding in complex media

“…Several published studies reported DSC analysis of a number of different viruses showing diagnostically unique thermograms that provide an additional means of their characterization, [28][29][30][31]. Unique thermograms for different viruses could be due to differences in the array of proteins that typically decorate viral coat surfaces [30].…”

Turnip yellow mosaic virus: transfer RNA mimicry, chloroplasts and a C‐rich genome

“…Similar capsid forms (artificial top components, ATCs) can be made by freeze‐thawing (Böttcher and Crowther, 1996; Kaper and Siberg, 1969) and by exposure to conditions such as elevated pH, temperature or pressure. The resultant empty shells differ somewhat according to their mode of origin, but all are distinct from the NTC empty shells, which have no holes (Michels et al ., 1999). High‐resolution structural studies on ATCs are needed to understand how virions are destabilized during decapsidation.…”

The RNA of turnip yellow mosaic virus exhibits icosahedral order

“…This is composed of native or near native protein capsids that lack RNA (Matthews, 1960). A preparation of particles identical in most respects to this top component can be made by thawing intact virions from liquid nitrogen temperatures (Kaper and Siberg, 1969) or by other means such as pH change (Keeling and Matthews, 1982) and high pressure (Leimkuhler et al, 2001) (for reviews, see references (Givord et al, 1972;Kaper, 1975;Michels et al, 1999)). These other preparations are collectively referred to as artificial top component (ATC).…”