Analysis of internal motions of RNase T1 complexed with a productive substrate involving ¹⁵N NMR relaxation measurements

The backbone dynamics of RNase T1 in the presence of exo-guanosine 2′,3′-cyclophosphorothioate (exo-cGPS isomer), which is a productive substrate, and in the presence of 3′-guanylic acid (3′GMP), which is an nonproductive substrate, were examined using ¹⁵N nuclear magnetic resonance. Although the X-ray crystal structure suggests that the modes of binding of these substrates to the active-site cleft are very similar, the order parameters in a number of regions in RNase T1 complexed with exo-cGPS isomer were different from those with 3′GMP. Moreover, the chemical exchange in line width observed for RNase T1 complexed with exo-cGPS isomer was also different from that observed for RNase T1 complexed with 3′GMP. From these results, we concluded that the internal motions in RNase T1 complexed with a productive substrate were not always identical to those in RNase T1 complexed with a nonproductive substrate.