Simultaneous processing of solid-state NMR relaxation and 1D-MAS exchange data: the backbone dynamics of free vs....

Two types of dynamic solid-state NMR experiments-relaxation and 1D-MAS exchange-were combined for the investigation of the backbone dynamics of a 15% randomly 15N-enriched protein barstar in both free and binase-bound states. The main novelty of this work is a simultaneous quantitative processing of the results of these two types of experiments that we call Simultaneous Relaxation and Exchange Data Analysis (SREDA) approach. It extends the well-known model-free approach such that it permits to discriminate between various motional models (jumps between different sites, wobbling in a cone, etc.). This objective cannot be achieved by analyzing the relaxation or exchange data separately. The SREDA approach was applied to probe a modification of the average backbone dynamics of barstar upon forming a complex with another protein binase. T(1) and off-resonance T(1rho) relaxation times of 15N backbone nuclei were measured at three temperatures between 0 and 45 degrees C, 1D-MAS exchange (CODEX) data were obtained at room temperature within the mixing time range from 0.3 to 200 ms. It has been found that the barstar backbone participates in two molecular processes with correlation times in the 10(-9)-10(-7) and 10(-3)-10(-2) s ranges. Forming the complex with binase results in a significant decrease of the amplitudes of both motions, suggesting that the complex is a more rigid and stable structure than free barstar.