Deuterium spin relaxation of fractionally deuterated ribonuclease H using paired 475 and 950 MHz NMR spectrometers

Deuterium ( 2 H) spin relaxation of 13 CH 2 D methyl groups has been widely applied to investigate picosecond-to-nanosecond conformational dynamics in proteins by solution-state NMR spectroscopy. The B 0 dependence of the 2 H spin relaxation rates is represented by a linear relationship between the spectral density function at three discrete frequencies J (0), J ( ω D ) and J (2 ω D ). In this study, the linear relation between 2 H relaxation rates at B 0 fields separated by a factor of two and the interpolation of rates at intermediate frequencies are combined for a more robust approach for spectral density mapping. The general usefulness of the approach is demonstrated on a fractionally deuterated (55%) and alternate 13 C- 12 C labeled sample of E. coli RNase H. Deuterium relaxation rate constants ( R 1 , R 1 ρ , R Q , R AP ) were measured for 57 well-resolved 13 CH 2 D moieties in RNase H at 1 H frequencies of 475 MHz, 500 MHz, 900 MHz, and 950 MHz. The spectral density mapping of the 475/950 MHz data combination was performed independently and jointly to validate the expected relationship between data recorded at B 0 fields separated by a factor of two. The final analysis was performed by jointly analyzing 475/950 MHz rates with 700 MHz rates interpolated from 500/900 MHz data to yield six J ( ω D ) values for each methyl peak. The J ( ω ) profile for each peak was fit to the original ( τ M , S f 2 , τ f ) or extended model-free function ( τ M , S f 2 , S s 2 , τ f , τ s ) to obtain optimized dynamic parameters.