CD and NMR studies on the conformational thermostability of 2-thioribothymidine found in the TψC loop of thermophile tRNA

Abstract

The intensities of the main CD bands of 2-thiouridine derivatives are from five to ten times stronger than those of uridine derivatives, suggesting a conformational ‘rigidity’ of the nucleoside unit of 2-thiouridine derivatives. 270 MHz proton NMR spectra of 2-thioribothymidine and ribothymidine were measured and fractional populations of the 3′- endo and gauche-gauche (gg) forms at 23–93°C were obtained. The enthalpy and entropy differences between the 2′- endo and 3′- endo forms of 2-thioribothymidine were determined as 1.0 kcal/mole and 1.3 eu, respectively. This inherent stability of the 3′- endo-gg-anti form of 2-thioribothymidine residue possibly contributes to the thermostability of thermophile tRNA's.