Dynamics of Reassembled Thioredoxin Studied by Magic Angle Spinning NMR: Snapshots from Different Time Scales
Jun Yang†§, Maria Luisa Tasayco‡ and Tatyana Polenova†
Solid-state NMR spectroscopy can be used to probe internal protein dynamics in the absence of the overall molecular tumbling. In this study, we report 15N backbone dynamics in differentially enriched 1−73(U-13C,15N)/74−108(U-15N) reassembled thioredoxin on multiple time scales using a series of 2D and 3D MAS NMR experiments probing the backbone amide 15N longitudinal relaxation, 1H−15N dipolar order parameters, 15N chemical shift anisotropy (CSA), and signal intensities in the temperature-dependent and 1H T2′-filtered NCA experiments. The spin-lattice relaxation rates R1 (R1 = 1/T1) were observed in the range from 0.012 to 0.64 s−1, indicating large site-to-site variations in dynamics on pico- to nanosecond time scales. The 1H−15N dipolar order parameters, S, and 15N CSA anisotropies, δσ, reveal the backbone mobilities in reassembled thioredoxin, as reflected in the average S = 0.89 ± 0.06 and δσ = 92.3 ± 5.2 ppm, respectively. From the aggregate of experimental data from different dynamics methods, some degree of correlation between the motions on the different time scales has been suggested. Analysis of the dynamics parameters derived from these solid-state NMR experiments indicates higher mobilities for the residues constituting irregular secondary structure elements than for those located in the α-helices and β-sheets, with no apparent systematic differences in dynamics between the α-helical and β-sheet residues. Remarkably, the dipolar order parameters derived from the solid-state NMR measurements and the corresponding solution NMR generalized order parameters display similar qualitative trends as a function of the residue number. The comparison of the solid-state dynamics parameters to the crystallographic B-factors has identified the contribution of static disorder to the B-factors. The combination of longitudinal relaxation, dipolar order parameter, and CSA line shape analyses employed in this study provides snapshots of dynamics and a new insight on the correlation of these motions on multiple time scales.