The thermal stability and decapsidation mechanism of tymoviruses: A differential calorimetric study

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

“… Variation with pH of the transition temperatures of empty shells. TYMV NTC (○), ATC‐A (×), ATC‐F (▵ for T1, ▴ SWA for T2), ATC‐P (□ for T1, ▪ for T2), and TYMV‐B (* for T1, + for T2; the third transition of TYMV‐B occurred at the same temperature as the unique transition of NTC or ATC‐A, at the same pH; data taken from [13]). Lines are only drawn as guides.…”

“…In contrast, upon continuous heating of TYMV‐B at pH 7.6 from 20 °C to 90 °C, the protein shells that formed at ≈ 50 °C collapsed at ≈ 58–60 °C, as did ATC‐F and ATC‐P. (At lower pH, virions are stabilized by strong RNA–protein interactions and decapsidate at higher temperatures only; for discussion, see [13]. ) The DSC profiles of a TYMV‐B sample at pH 7.6 did not depend upon the scan rate in the interval 0.25–2 °C·min −1 [13].…”

“…(At lower pH, virions are stabilized by strong RNA–protein interactions and decapsidate at higher temperatures only; for discussion, see [13]. ) The DSC profiles of a TYMV‐B sample at pH 7.6 did not depend upon the scan rate in the interval 0.25–2 °C·min −1 [13]. However, when a sample that was first heated to 55 °C at 1 °C·min −1 was scanned again in the microcalorimeter after having been kept overnight at 4 °C, the peak of the thermogram corresponding to the collapse of the shells became very broad, and its maximum shifted to ≈ 65 °C (not shown).…”

“…ATC‐A resulted from alkaline titration of a 3.5 mg·mL −1 solution of TYMV‐B in 1 m KCl at pH 11.55 for 30 min at 30 °C, under nitrogen atmosphere, the reaction being stopped by rapid titration to pH ≤ 8.0 [21]. ATC‐T was obtained by heating a 5 mg·mL −1 solution of TYMV‐B in 0.01 m sodium phosphate buffer pH 7.6–55 °C at a rate of 1 °C·min −1 , the reaction being stopped by addition (v/v) of ice‐cold buffer [13]. ATC‐U was prepared by 5 min incubation at 37 °C of a 5 mg·mL −1 virus solution in 8 m urea, 1 m NaCl, 0.01 m sodium phosphate buffer pH 7.2 [22].…”

“…[12] investigated the thermostability of both TYMV virions and empty shells in Tris/HCl buffer and concluded that histidine residues play a major role in the dependence of the stability of TYMV on pH. Using buffers with as small as possible a temperature dependence of their pH, and controlling the fate of the particles by electron microscopy and analytical ultracentrifugation, it has been shown that TYMV‐B decapsidates in three irreversible steps [13]. TYMV‐B first releases its RNA (probably through a hole in the capsid), and this step is accompanied by an exothermic process that may correspond to a conformational change of the shell preceding decapsidation, as was also observed upon expansion of the shell of phage P22 [14,15].…”